H 



5 LIBRARY OF CONGRESS. 



V 



[SMITHSONIAN DEPOSIT.] 

/64g I 

| UNITED STATES OF AMERICA * 



THE 



PLANETARY 



AND 



STELLAR WORLDS: 

A POPULAR EXPOSITION 

OF THE 

GREAT DISCOVERIES AND THEORIES 

OF 

MODERN ASTRONOMY. 

IN A SERIES OF TEN LECTURES. 

BY 0. M^MITCHEL, A.M. 
»* 

DIRECTOR OF THE CINCINNATI OBSERVATORY. 



NEW YORK: 
BAKER & SCRIBNER, 

36 PARK ROW, AND 145 NASSAU St. 



s^mu^? 



QS5\ 



Entered, 


according to Act of Congress, in the year 1848, 
0. M. MITCHEL, 


by 


In the Clerk' 


s Office of the District Court for the District of Ohio. 



JAMES & CO., Stereotypes, Cincinnati. 



PREFACE. 



A few words in explanation of the circumstances under 
which this volume is presented to the public, may not be 
unacceptable to the reader. It is now a little more than six 
years since the writer conceived the idea of erecting a great 
astronomical observatory in the city of Cincinnati. My at- 
tention had been for many years directed to this subject, by 
the duties of the professorship, which I then held in the col- 
lege. In attempting to communicate the great truths of astro- 
nomy, there were no instruments at hand, to confirm and fix 
the wonderful facts recorded in the books. Up to that period 
our country, and the west particularly, had given but little 
attention to practical astronomy. A few individuals, with a 
zeal and ardor deserving of all praise, had struggled on to 
eminence almost without means or instruments. An isolated 
telescope was found here and there scattered through the 
country ; but no regularly organized observatory with power- 
ful instruments, existed within the limits of the United States, 
so far as I know. 

To attempt the building of an observatory of the first class, 
and to furnish it with instruments of the highest order, with- 
out any aid from the general or state government, but by the 
voluntary contribution of all classes of citizens, was an enter- 
prise of no common difficulty. To ascertain whether any 
interest could be excited in the public mind, in favor of astro- 
nomy, in the spring of 1842 a series of lectures was delivered 

(iii) 



IV PREFACE. 

in the hall of the Cincinnati College. To give an increased 
effect to these discourses (which were unwritten, and in a 
style of great simplicity), a mechanical contrivance was pre- 
pared, by the aid of which the beautiful telescopic views in 
the heavens were presented to the audience, with a brilliancy 
and power scarcely inferior to that displayed by the most 
powerful telescopes. To this fortunate invention were these 
lectures, no doubt, principally indebted for the interest which 
they produced, and which occasioned them to be attended by 
a very large number of the intelligent persons in the city. 
Encouraged by the large audiences, which continued through 
two months to fill the lecture-room, and still more by the 
request to repeat the last lecture of the course in one of the 
great churches of the city, I matured a plan for the building 
of an observatory, which it was resolved should be presented 
to the audience at the close of the lecture, in case circum- 
stances should favor. Through the kindness of a few friends, 
who were now beginning to take a deep interest in the matter, 
more than two thousand persons were in attendance ; and it 
seemed that the moment had arrived for taking the first step in 
an enterprise whose fate it was impossible to predict. 

Having closed the subject under discussion, the audience 
were requested to give me a few minutes of time, for the 
explanation of a matter which it was hoped would not be 
received without some feelings of interest and approbation. 
The rapid advances of astronomy in Europe were then referred 
to — the erection of observatories in all parts of the world — the 
variety of magnificent instruments in Russia and Germany, in 
France and England, and the utter deficiency of our own 
country in every thing pertaining to the science of the stars. 






PREFACE. V 

The past neglect was easily accounted for, and might be ex- 
cused ; the future scientific character of the country rested with 
the people, and upon them devolved the responsibility of pro- 
viding the means for original research. In Europe, imperial 
treasure and princely munificence could build the temples of 
science ; under a free government no such means existed, and 
to accomplish the erection of these great scientific institutions, 
the intelligent liberality of the whole community was the only 
resource. But it had been denied that this resource could be 
relied on ; and it had been roundly asserted that, in the nature 
of things, the United States must ever remain grossly defec- 
tive in all the appliances for scientific research. To test the 
truth or falsehood of these statements was not a difficult mat- 
ter ; and thus encouraged by the interest already manifested in 
behalf of astronomy, I had already resolved to devote five. 
years of faithful effort to accomplish the erection of a great 
astronomical observatory in the city of Cincinnati. 

This announcement was received with every mark of favor, 
and the following simple plan was at once presented. The 
entire amount required to erect the buildings and purchase the 
instruments, should be divided into shares of twenty-five dol- 
lars ; every shareholder to be entitled to the privileges of the 
observatory, under the management of a board of control, to 
be elected by the shareholders. Before any subscription 
should become binding, the names of three hundred subscribers 
should be first obtained. This accomplished, these three hun- 
dred should meet, organize, and elect a board, who should 
thenceforward manage the affairs of the association. 

Such is the history of the origin of the Cincinnati Astrono- 
mical Society. Two resolutions were taken in the outset, to 
a2 



VI PREFACE. 

which I am indebted for any success which may have attended 
my own personal efforts. First : To work faithfully for five 
years, during all the leisure which could be spared from my 
regular duties. Second : Never to become angry, under any 
provocation, while in the prosecution of this enterprise. 

In three weeks the three hundred subscribers had been ob- 
tained. No public meeting had been called ; and these names 
had been procured by private solicitation, and a personal 
explanation of the nature and advantages of the enterprise. So 
soon as the number was complete, the subscribers convened, 
organized, elected officers and a directory, and gave me a com- 
mission to visit Europe, to procure instruments, examine ob- 
servatories, and obtain the requisite knowledge to erect and 
conduct the institution which it was now hoped would be one 
day reared. 

This order being received, on the second day I started for 
New York, and on the 16th of June, 1842, sailed for Liver- 
pool. Having visited many of the best appointed observa- 
tories both in England and on the continent (in each and 
every one of which I was received with a degree of kindness 
and attention for which I acknowledge the deepest obligations), 
and having been unsuccessful in finding, either in London or 
Paris, an object-glass of the size required, I finally determined 
to visit the city of Munich. The fame of the optical insti- 
tute of the celebrated Frauenhofer had even reached the banks 
of the Ohio ; and it was hoped that, in that great manufactory, 
an instrument such as the society desired might be obtained, 
if not completed, at least in such a state of forwardness as to 
permit it to be furnished at an early day. In this I was not 
disappointed. An object-glass of nearly twelve inches diame- 



PREFACE. Vll 

ter, and of superior finish, was found in the cabinet of M. 
Mertz, the successor of Frauenhofer. This glass had been 
subjected to a severe trial in the tube of the great refractor of 
the Munich observatory, by Dr. Lamont, and had been pro- 
nounced of the highest quality. 

To mount this glass would require about two years, at a 
cost of nearly ten thousand dollars ; a sum considerably 
greater than that appropriated at the time for an equatorial 
telescope. Having made a conditional arrangement for this 
and other instruments, I returned to Greenwich, England, 
where, at the invitation of Professor Airy, the Astronomer 
Royal, I remained for some time to study. Having accom- 
plished the objects of my journey, I returned home, and ren- 
dered a report to a very large meeting of the members of the 
association and other citizens of Cincinnati. 

During my absence of four months, a great change had 
occurred in the commercial affairs of the country. Every 
thing was depressed to the lowest point, and increased in a 
high ratio the necessary difficulties of such an undertaking ; 
always great, even if carried forward at a time when the 
country is prosperous. 

With great difficulty the subscription was increased to an 
amount sufficient to warrant the ordering of the great object- 
glass already referred to. The sum of three thousand dollars 
was collected and remitted to meet the first payment. Even 
this fraction of the entire sum was collected with difficulty ; 
but as the remaining part of the price of the telescope was not 
to be paid until the completion of the instrument, it was hoped 
that the ample time thus allowed would render the task of 
collection comparatively easy. 



Vlll PREFACE. 

The principal instrument having been ordered, and the first 
payment on its cost made, attention was now given to the pro- 
curing of a suitable site for the building. Fortunately for the 
society, the place of all others most perfectly adapted to their 
wants, was then the property of Nicholas Longworth, Esqr. 
It is a lofty hill-top, rising some four hundred feet above the 
level of the city, and commanding a perfect horizon in all 
directions. On making known to Mr. Longworth the pros- 
pects and wants of the Astronomical Society, the writer was 
directed by him to select four acres on the hill-top, out of a 
tract of some twenty-five acres, and to proceed at once to en- 
close it, as it would give him great pleasure to present it to 
the association. On compliance with the conditions of the 
title-bond, a deed has since been received, placing the society 
in full possession of this elegant position. 

Preparations were now made to commence the erection of 
the building for the observatory. The grounds were enclosed, 
a road built, rendering the access to the hill-top comparatively 
easy, the excavations for the foundations were made, and, on 
the 9th day of November, 1843, the corner-stone of the pier 
which was to sustain the great Refracting Telescope, was 
laid by John Quincy Adams, with appropriate ceremonies. 
On this occasion Mr. Adams made his last great oration. The 
deep interest which he had taken in astronomical science, 
warranted the hope that he might be induced to visit the west, 
on the occasion of laying the foundation-stone of the first great 
popular observatory ever erected in the United States. This 
hope was not disappointed. The unaffected devotion of this 
truly great man to the interests of his country, were, perhaps, 
never more perfectly exhibited than in his ready acquiescence 



PREFACE. IX 

to comply with the wishes of the astronomical society, that he 
should perform for them the important services on which the 
future success of this new enterprise in no small degree de- 
pended. His high character, his advanced age, the length of 
the journey, the inclemency of the season, all combined to 
exhibit to his countrymen the depth of his interest in a cause 
which could induce such sacrifices. 

After the laying of the corner-stone, the lateness of the 
season, and other causes, induced a suspension of the work on 
the building for the winter ; and it was not resumed until May, 
1844. In the mean time, after incredible difficulty, the entire 
amount called for in the payment for the great telescope, 
was collected and remitted ; and the society was left with 
scarcely a dollar of available means, to commence the erection 
of a building which, according to the plan, would cost some 
seven or eight thousand dollars. 

It was believed that the intelligent mechanics of Cincinnati 
would lend their powerful aid in the accomplishment of an 
enterprise which had progressed far enough to give some con- 
fidence in its ultimate success. With little or no means the 
building was commenced, trusting to activity and perseverance 
to supply the means as the work progressed. During the 
first week but three workmen were employed ; but by the 
commencement of the next week the funds had been obtained 
to pay these, and to double their number. In six weeks not 
less than one hundred hands were at work on the hill-top and 
in the city. Mechanics of all trades subscribed for stock, and 
paid their subscription in work. The stone of which the 
building is erected, was quarried from the grounds of the 
society. The lime was burnt on the hill, and every means 



X PREFACE. 

was adopted to reduce the necessary expenditure. Payment 
for stock in the society was received in every possible article 
of trade ; due-bills were taken, and these were converted into 
others which would serve in the payment of bills. 

In this way the building was reared, and finally covered in, 
without incurring any debt. But the conditions of the bond, 
by which the lot of ground was held, required the completion 
of the observatory in two years from its date ; and these two 
years would expire in June, 1845. It was seen to be impos- 
sible to carry forward the building fast enough to secure its 
completion by the required time, without incurring some debt. 
My own private resources were used, in the hope that a short 
time after the finishing of the observatory would be sufficient 
to furnish the funds to meet all engagements. The work was 
pushed rapidly forward. In February, 1845, the great tele- 
scope safely reached the city of Cincinnati ; and in March the 
building was ready for its reception. I had now exhausted 
all my private means, and, to increase the difficulty of the 
position in which I was placed, the College edifice took fire 
and burned to the ground. My ordinary means of support 
were thus destroyed at a single blow. I had engaged to con- 
duct the observatory, without compensation from the society, 
for ten years, in the hope that my college salary would be suf- 
ficient for my wants. It was impossible to abandon the 
observatory. The college could not be rebuilt, at least for 
several years, and in this emergency I found it necessary to 
seek some means of support, least inconsistent with my duties 
in the observatory. My public lectures at home had been 
comparatively well received, and after much hesitation it was 
resolved to make an experiment elsewhere. For five years I 



PREFACE. XI 

had been pleading the cause of science among those little 
acquainted with its technical language. I had become habitu- 
ated to the use of such terms as were easily understood ; and 
probably to this circumstance, more than to any other one 
thing, am I indebted for any success which may have attended 
my public lectures. To the citizens of Boston, Brooklyn, 
New York, and New Orleans, for the kindness with which 
they were pleased to receive my imperfect efforts, I am deeply 
indebted. My lectures were never written, and no idea was 
entertained of publishing a course, until the partiality of my 
friends induced me to attempt this experiment. 

Such are the circumstances under which this effort to trace 
the career of the human mind, in its researches among the 
stars, has been undertaken. No one science, perhaps, so per- 
fectly illustrates the gradual growth and development of the 
powers of human genius. The movement of the mind has 
been constantly onward — its highest energies have ever been 
called into requisition — and there never has been a time when 
astronomy did not present problems not only equal to all that 
man could do, but passing beyond the limits of his greatest 
intellectual vigor. Hence, in all ages and countries, the abso- 
lute strength of human genius may be measured by its reach 
to unfold the mysteries of the stars. 

It will be seen that in the following lectures one single 
object has engaged the attention of the writer — the structure 
of the universe, so far as revealed by the mind of man. 
The uses of science have in no way been considered. The 
effects on the mind, on society, on civilization, on commerce, 
on religion, have not been permitted to mar the unity of the 
original design. The onward, steady, triumphant march of 



Xll PREFACE. 

mind, in its study and exploration of the universe of God, has 
been my only object, the single theme of the entire series. 

I may be pardoned for a single word, before taking leave of 
the reader, touching the condition of our country with refer- 
ence to practical astronomy. Within a few years an entire 
revolution on this subject has occurred. The reproach which 
once rested on the United States has been removed. Several 
magnificent instruments now adorn the observatories of the 
New World, and the contributions of American astronomers, 
to science, are beginning to change the scientific character of 
our country in the eyes of the old World. It is gratifying 
to know that several institutions, with ample means of support, 
now exist in our country, to which the interests of American 
science are committed with entire confidence. The obser- 
vatories at Washington, Cambridge, Philadelphia, and George- 
town, are amply provided with instruments, and an efficient 
corps of observers are constantly occupied in their use. 

For a long time to come, one principal object will engage 
the instruments of the Cincinnati observatory, viz., the explo- 
ration of the heavens south of the equator, and the re-measure- 
ment of Striive's double stars in that region. Should this work 
progress but slowly, let it be remembered that the director of 
the observatory has no assistant, out of his own immediate 
family, and must devote a large portion of his time to other 
duties, far more closely allied to the earth than the stars. 

Cincinnati Observatory, 

Mount Adams, May, 1848. 



TABLE OF CONTENTS 



LECTURE I. 



AN EXPOSITION OF THE PROBLEM WHICH THE HEAVENS PRE- 
SENT FOR SOLUTION. 

First revolution of the Heavens witnessed by man, 18. The 
curiosity excited and its effects, 19. Object of the course, 20. 
The astronomer lives in all ages, 22. First problem to distinguish 
between real and apparent motion, 23. The relations of the sun, 
and earth, and moon, 24. The wandering stars or planets, 25. 
Fixed stars, points of reference, 27. Complexity of the planetary 
movements, 28. Discovery of the true center of motion, 29. The 
planets form a system; their orbits, laws, stability, 31. Pertur- 
bations, 32. Analytic machinery, 33. Examination of the starry 
heavens, 34. Distance of the fixed stars to be determined, 35. 
Motions among the stars, 36. The binary systems; movement 
of the sun in space, 37. Investigations yet to be made, and pro- 
bable success, 39. 

LECTURE II. 

THE DISCOVERIES OF THE PRIMITIVE AGES. 

The founder of the science of astronomy unknown, 42. First 
discovery on the moon, 43. Her motion among the stars and her 
phases, 44. Cause of the phases sought; two revolutions of the 
moon discovered, 45. First ideas of the constellations; North 
Star, 47. 3!otions of the sun and moon among the stars ; the 
starry heavens surround the earth, 48. First measure of the year, 
49. A moving star discovered, 50. Periods of the planets deter- 
mined, 53. The sun's apparent motion the subject of perplexity, 
55. The equinoxes and solstices, 56. Inequality in the sun's 
motion detected, 57. The construction of the sphere, 58. Its 
uses in observing, 59. Eclipses of the sun and moon and their 
effects, 60. Explanation of solar eclipses; discovery of the moon's 
reflective light, and explanation of her phases, 6 1 . Lunar eclipses 
explained; prediction of the first eclipse, 65. Value of recorded 
eclipses, 68. 

B CxiiO 



XIV TABLE OF CONTENTS. 

LECTURE III. 

THEORIES FOR THE EXPLANATION OF THE MOTIONS OF THE 
HEAVENLY BODIES. 

The names of early discoverers lost, 70. Chaldean period 
found among many nations; the days of the week, and their names, 
place of the vernal equinox, 71. Precession of the equinoxes, 73. 
Astronomy of the primitive ages, and condition of the mind at the 
beginning of the era reached by history, 75. Causes retarding 
the progress of astronomy, 77. The confounding of true and 
apparent motion; immobility of the earth and its central position, 
78. The Greek astronomers, Pythagoras, Nicetas, Hipparchus, 
Ptolemy, 80. System of Ptolemy, 82. Astronomy cultivated by 
the Arabs, 82. The era of modern science commences, 84. Co- 
pernicus and his discoveries, 86. His system promulged with 
great caution, 87. Kepler, the character of his mind, his mode 
of research, 91. His great discoveries; he finds the orbits of the 
planets, 92. Detects his second law, 93. His efforts to fin.d the 
third law successful. 98. Importance of these laws, 99. 

LECTURE IV. 

DISCOVERY OF THE GREAT LAWS OF MOTION AND GRAVITATION. 

The philosophy of Aristotle — its hold on the mind, 101. Cha- 
racteristics of Galileo's mind, 102. He detects the errors of Aris- 
totle, 103. Attacks his theories, and demonstrates their falsehood 
by experiment, 104. Driven from Pisa by his enemies, 105. 
Discovers the law of falling bodies, 106. Adopts the Copernican 
theory, 107. Constructs a telescope, 108. His discoveries in the 
moon, and among the planets and fixed stars, 110. Phases of 
Venus, 111. Questions relating to the planetary motions, 113. 
Laws of motion; the centrifugal force, 114. Problem presented 
for solution to Newton, 116. Discoveries of Descartes; conjec- 
tures of Kepler, 117. Measure of the moon's distance and of the 
earth's circumference, 118. The law of gravitation — Newton's 
first effort to demonstrate the truth of this law, 121. He finally 
shows that the moon is ever falling towards the earth, and proves 
the law, 124. Enunciation of his great law, 125. Discovers 
that the planets may revolve in conic sections, 126. Contrast 
between Kepler's and Newton's methods of research, 128. 

LECTURE V. 

UNIVERSAL GRAVITATION APPLIED TO THE EXPLANATION OF 
THE PHENOMENA OF THE SOLAR SYSTEM. 

The era of physical astronomy commences, 132. A theoretic 
system proposed and discussed; a central sun and solitary planet, 



TABLE OF CONTENTS. XV 

133. Planets and satellites added and their effects considered, 
136. How the imagined system may be made the system of na- 
ture, 137. Discussion of the relative motions of the sun, moon 
and earth, under the action of their mutual influences, 139. The 
moon's acceleration ; motion of her apsides, nodes, &c, and the 
discovery of the change in the figure of the earth's orbit, 146. 
Perplexity occasioned by the seeming discrepancy between the 
observed and computed motion of the moon's perigee, 149. Fi- 
nally removed by Clairault, 150. Changes in the earth's figure 
occasioned by its rotation, 153. The form of equilibrium reached, 
155. The precession of the equinoxes caused by the protuberant 
matter at the earth's equator, 157. Moon affected by the re- 
dundant matter at the earth's equator, 160. Wonderful questions 
answered by an examination of the moon, 161. 

LECTURE VI. 

THE STABILITY OF THE PLANETARY SYSTEM. 

Rapid survey of the system, 165. General characteristics of 
the planets, 166. What phenomena gravitation must account for, 
167. Stability not the sole object of the Creator, 168. Laws of 
matter selected in wisdom, 170. By how much does the central 
force diminish the primitive velocity of a planet] 171. Changes 
in the elements of the orbits of the planets, 174. The eccentri- 
city, 175. Stability of the principal axes, 176. Motion of the 
perihelion, 177. The inclinations, 180. The lines of nodes, 181. 
The periodic times, 183. Stability of the great system, 185. Of 
the system of the earth and moon, 186. Of Jupiter's system, 
187. Of Saturn's system, 190. 

LECTURE VII. 

THE DISCOVERY OF THE NEW PLANETS. 

Kepler's speculations, 194. Discovery of Uranus, 195. Bode's 
law of interplanetary spaces, 196. The astronomical congress 
of Lilienthal, in 1800, 198. Piazzi's discovery of a new planet, 
Ceres ; its loss and rediscovery, 200. The symmetry of the sys- 
tem destroyed by the discovery of Pallas, 201. Olbers's theory of 
the bursting of a planet, 202. Discovery of Juno and Vesta, 203. 
Hen eke discovers Astrea and Hebe, 204. Hind discovers Iris 
and Flora, 204. Search for a planet beyond Uranus commenced, 
206. Causes of this search, 207. Leverrier's researches on Mer- 
cury, 209. Its transit in May, 1845,211. Leverrier presents his 
computations to .the French Academy, 212. Popular exhibition 
of his reasoning, 215. The hypothetical planet found by Galle, 
of Berlin, 216. Adams's computations, 217. The new planet 
detected by its disc, 218. Walker's computations, 219. Pierce's 
views, 221. Leverrier claims Neptune to be the planet of 
theory. 



XVI TABLE OF CONTENTS. 

LECTURE VIII. 

THE COMETARY WORLDS 

Characteristics of comets, 223. Reduced to law by Newton, 
225. The comet of 1680,226. Halley's comet of 1682,227. Its 
return in 1759 predicted, 229. Its return in 1835,231. Won- 
derful changes in its magnitude, 233. Encke's comet, 235. Ap- 
proaching the sun, 236. Resisting medium, 237. Biela's comet, 
238. Fears excited of collision with the earth, in 1832,239. Its 
nebulous character, 240. Its double character in 1846. Sepa- 
ration of the comets, 242. Vast periods of some comets, 244. 
Comets seen to transit the sun's disc, 246. Comets accounted for 
by Laplace's nebular hypothesis, 247. Herschel's theory of the 
physical condition of comets, 250. His theory accounts for the 
diminishing period of Encke's comet, 251. Zodiacal light, 252. 

LECTURE IX. 

THE SCALE ON WHICH THE UNIVERSE IS BUILT. 

Scale of the planetary system, 253. Radius of the earth's orbit 
too small a unit, 254. The velocity of light determined from the 
eclipses of Jupiter's satellites, and employed as a unit, 256. 
Parallax of the fixed stars, 258. No parallax sensible to the 
naked eye, 260. Great distance of the fixed stars inferred from 
this fact, 261. Bradley's researches for parallax, 263. Discovery 
of nutation and its value, 264. Discovery of aberration — its 
explanation, 266. Herschel's researches for parallax, 269. Dis- 
covery of the revolving stars, 270. Power of modern telescopes, 
271. Bessel discovers the parallax of 61 Cygni, 273. 

LECTURE X. 

THE MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 
Distances separating man from the stars, 290. Various diffi- 
culties in the research for their motions, 291. Hipparchus dis- 
covers a new and brilliant star, 292. The new star of 1572, 293. 
The new star of 1604, 294. The disappearance of old stars, 295. 
Changes of Algol, 295. Periodical stars, 296. Gravitation ex- 
tended to the sphere of the fixed stars, 297. Periods of some of 
the binary systems, 298. Herschel sounds the depth of the Milky 
Way, 299. Seeks the direction of the solar motion, 300. His 
reasoning, 302. Argelander's research for the point towards 
which the solar system is moving, 306. Struve's investigation 
for the quantity of angular motion of the system, as seen from 
stars of the first magnitude, 308. His father's research for the 
relative distances of stars of different magnitudes, 310. Peters's 
research for the parallax of stars of the second magnitude, 311. 
Maedler's theory of the central sun, 319. The attributes of God. 
as displayed in the universe, 324. 



THE 

STRUCTURE OF THE UNIVERSE 



INTRODUCTORY LECTURE. 



AN EXPOSITION OF THE PROBLEM WHICH THE HEAVENS 
PRESENT FOR SOLUTION. 

The subject to which your attention is invited, 
claims no specific connexion with the every day 
struggle of human life. Far away from the earth on 
which we dwell, in the blue ocean of space, thou- 
sands of bright orbs, in clusterings and configura- 
tions of exceeding beauty, invite the upward gaze of 
man, and tempt him to the examination of the won- 
derful sphere by which he is surrounded. The starry 
heavens do not display their glittering constellations 
in the glare of day, while the rush and turmoil of 
business incapacitate man for the enjoyment of their 
solemn grandeur. It is in the stillness of the mid- 
night hour, when all nature is hushed in repose, when 
the hum of the world's on going is no longer heard, 
that the planets roll and shine, and the bright stars, 
trooping through the deep heavens, speak to the wil- 
ling spirit that would learn their mysterious being. 

Often have I swept backward in imagination six 
thousand years, and stood beside our Great Ances- 

B2 (17) 



18 STRUCTURE OF THE UNIVERSE. 

tor, as he gazed for the first time upon the going 
down of the sun. What strange sensations must 
have swept through his bewildered mind, as he watch- 
ed the last departing ray of the sinking orb, uncon- 
scious whether he should ever behold its return. 
Wrapt in a maze of thought, strange and startling, 
his eye long lingers about the point at which the 
sun had slowly faded from his view. A mysterious 
darkness, hitherto unexperienced, creeps over the face 
of nature. The beautiful scenes of earth, which 
through the swift hours of the first wonderful day of 
his existence, had so charmed his senses, are slowly 
fading one by one from his dimmed vision. A gloom 
deeper than that which covers earth, steals across the 
mind of earth's solitary inhabitant. He raises his 
inquiring gaze towards heaven, and lo ! a silver 
crescent of light, clear and beautiful, hanging in the 
western sky, meets his astonished eye. The young 
moon charms his untutored vision, and leads him up- 
ward to her bright attendants, which are now steal- 
ing one by one, from out the deep blue sky. The 
solitary gazer bows, and wonders, and adores. The 
hours glide by — the silver moon is gone — the stars are 
rising — slowly ascending the heights of heaven — and 
solemnly sweeping downward in the stillness of 
the night. The first grand revolution to mortal vision 
is nearly completed. A faint streak of rosy light is 
seen in the east — it brightens — the stars fade — the 
planets are extinguished — the eye is fixed in mute 
astonishment on the growing splendor, till the first 
rays of the returning sun dart their radiance on the 
young earth and its solitary inhabitant. To him " the 
evening and the morning were the first day." 



INTRODUCTORY LECTURE. 19 

The curiosity excited on this first solemn night — the 
consciousness that in the heavens God had declared 
his glory — the eager desire to comprehend the mys- 
teries that dwell in these bright orbs, have clung to 
the descendants of him who first watched and won- 
dered, through the long lapse of six thousand years. 
In this boundless field of investigation, human genius 
has won its most signal victories. — Generation after 
generation has rolled away, age after age has swept 
silently by, but each has swelled by its contribution 
the stream of discovery. — One barrier after another 
has given way to the force of intellect — mysterious 
movements have been unravelled — mighty laws have 
been revealed — ponderous orbs have been weighed, 
their reciprocal influences computed, their complex 
wanderings made clear, until the mind, majestic 
in its strength, has mounted step by step up the 
rocky height of its self-built pyramid, from whose star- 
crowned summit it looks out upon the grandeur of 
the universe, self-clothed with the prescience of a 
God. — With resistless energy it rolls back the tide 
of time, and lives in the configuration of rolling 
worlds a thousand years ago, or more wonderful, it 
sweeps away the dark curtain from the future, and 
beholds those celestial scenes which shall greet the 
vision of generations when a thousand years shall 
have rolled away, breaking their noiseless waves 
on the dim shores of eternity. 

To trace the efforts of the human mind in this 
long and ardent struggle, to reveal its hopes and 
fears, its long years of patient watching, its moments 
of despair and hours of triumph — to develop the means 
by which the deep foundations of the rock-built pyra- 



20 STRUCTURE OF THE UNIVERSE. 

mid of science have been laid, and to follow it as it 
slowly rears its stately form from age to age, until its 
vertex pierces the very heavens — these are the ob- 
jects, proposed for accomplishment, and these are the 
topics to which I would invite your earnest attention. 
The task is one of no ordinary difficulty. It is no 
feast of fancy, with music and poetry, with eloquence 
and art, to enchain the mind. Music is here — but 
it is the deep and solemn harmony of the spheres. 
Poetry is here — but it must be read in the characters 
of light, written on the sable garments of night. 
Architecture is here — but it is the colossal structure 
of sun and system, of cluster and universe. Eloquence 
is here — but " there is neither speech nor language. — 
Its voice is not heard," yet its resistless sweep comes 
over us in the mighty periods of revolving worlds. 

Shall we not listen to this music, because it is 
deep and solemn? Shall we not read this poetry, 
because its letters are the stars of heaven? — Shall 
we refuse to contemplate this architecture, because 
" its architraves, its archways, seem ghostly from in- 
finitude." Shall we turn away from this surging 
eloquence, because its utterance is made through 
sweeping worlds? No — the mind is ever inquisitive, 
ever ready to attempt to scale the most rugged steeps. 
Wake up its enthusiasm — -fling the light of hope on 
its pathway, and no matter how rough, and steep, 
and rocky it may prove, onward! is the word which 
charms its willing powers. 

It is not my wish or design to introduce you to 
the dark technicalities of science, neither do I propose 
to rest satisfied with the barren statement of the 
results which have been reached by the efforts of 



H 



INTRODUCTORY LECTURE. 21 

genius. While on the one hand I shall endeavor to 
shun all attempt at critical scientific demonstration, 
which could only be intelligible to the professed 
student of astronomy, I shall on the other hand 
fearlessly attempt such an exposition of the processes 
and trains of reasoning by which great truths have 
been elicited, as to show to every intelligent mind 
that the problem is not impossible ; by simplicity of 
language, by familiar illustrations, to fling light 
enough upon these mysterious propositions, to show 
a pathway, though it be dim and rugged, still a 
pathway, which if pursued shall certainly lead to a 
full and perfect solution. I ask, then, no critical 
previous knowledge of the subject, on the part of 
those who would follow me in the wonderful devel- 
opments which I am about to attempt. Give me 
but your earnest and unbroken attention. Go with 
me in imagination, and join in the nightly vigils of 
the astronomer, and while his mind with powerful 
energy struggles with difficulty, join your own sym- 
pathetic efforts with his — hope with his hope — trem- 
ble with his fears — rejoice with his triumphs. Lend 
me but this kind of interest, and my task is already 
half accomplished. 

Before proceeding to an actual exposition of the 
structure of the Heavens, I propose in this introductory 
lecture to announce the nature of the problem, which 
the mind has essayed to resolve, and to point out the 
more important auxiliaries, mental and mechanical, 
which it has conjured to its aid. If the difficulties of 
this problem should overwhelm the mind, let it be 
remembered that the astronomer has ever lived, and 
never dies. The sentinel upon the watchtower is 



22 STRUCTURE OF THE UNIVERSE. 

relieved from duty, but another takes his place, and 
the vigil is unbroken . No — the astronomer never dies . 
He commences his investigations on the hill tops of 
Eden — he studies the stars through the long centuries 
of antideluvian life. The deluge sweeps from the 
earth its inhabitants, their cities and their monu- 
ments — but when the storm is hushed, and the heav- 
ens shine forth in beauty, from the summit of Mount 
Arrarat the astronomer resumes his endless vigils. 
In Babylon he keeps his watch, and among the Egyp- 
tian priests he inspires a thirst for the sacred mys- 
teries of the stars. The plains of Shinar — the temples 
of India — the pyramids of Egypt, are equally his 
watching places. When science fled to Greece, his 
home was in the schools of her philosophers; and 
when darkness covered the earth for a thousand 
years, he pursues his never ending task from amidst 
the burning deserts of Arabia. When science dawn- 
ed on Europe, the Astronomer was there — toiling with 
Copernicus — watching with Tycho — suffering with Ga- 
lileo — triumphing with Kepler. Six thousand years 
have rolled away since the grand investigation com- 
menced. We stand at the terminus of this vast pe- 
riod, and looking back through the long vista of de- 
parted years, mark with honest pride the successive 
triumphs of our race. Midway between the past and 
future, we sweep backward and witness the first rude 
effort to explain the celestial phenomena — we may 
equally stretch forward thousands of years, and al- 
though we cannot comprehend what shall be the 
condition of astronomical science at that remote pe- 
riod, of one thing we are certain — the past, the pre- 
sent, and the future, constitute but one unbroken 



INTRODUCTORY LECTURE. 



chain of observations, condensing all time, to the 
astronomer, into one mighty now. 

From the vantage ground which we occupy, it will 
not be difficult to announce so much of the great 
problem as has already been resolved, and to form 
some approximate conception of what remains for 
future ages to accomplish. 

In the exposition about to be attempted, I do not 
propose, to present any trains of reasoning, or any 
results which may have been reached. These shall 
engage our attention hereafter. At present permit 
me simply to translate into language the questions 
which the visible heavens propound. 

The most cursory examination of the celestial 
vault reveals the fact, that not one solitary object, 
visible to the eye, is at rest. Motion is the attribute 
of sun and moon and planets and stars. The earth 
we inhabit alone remains fixed, to the senses. 

The first great problem propounded for human 
ingenuity, is to sever real motion from that which is 
unreal and only apparent. To accomplish this, some 
knowledge of the form of the earth which we inhabit 
must be obtained. Not only must we acquire a 
knowledge of its figure, but in like manner we must 
learn with certainty its actual condition, whether of 
rest or motion. If at absolute rest in the centre of 
the universe, then the rising sun, the setting moon, 
the revolving heavens, are real exhibitions, and must 
be examined as such. On the contrary, should it be 
found to be impossible to predicate of the earth ab- 
solute immobility, then arises the complicated ques- 
tion, how many motions belong to it ? and with what 
velocity does it move ? If a motion of rotation exist, 



24 STRUCTURE OF THE UNIVERSE. 

what is the position of the axis about which it re- 
volves, and is this axis permanent or changeable? 
If a motion of translation in space must be adopted, 
then whither is the earth urging its flight ? what the 
nature of the path described ? the velocity of its move- 
ment, and the laws by which it is governed ? These 
are some of the questions which present themselves 
in the outset, touching the condition of the earth, on 
whose surface the astronomer is located, in his re- 
searches of the heavens. 

Beyond the limits of the earth, a multitude of ob- 
jects present themselves for examination: and first 
of all the sun, the great source of life and light and 
heat, demands the attention of the student of the 
heavens. That some inscrutable tie binds it to the 
earth, or the earth to it, was early recognised in the 
fact, that whether the sun was moving or at rest, 
the relative distance of it and the earth never changed 
by any great amount; and whatever changes did occur, 
were all obliterated in a short period and the distance 
by which these bodies are separated was restored to 
its primitive value, to recommence its cycle of changes 
in the same precise order. — Here then was a grand 
problem, to determine the relations existing between 
the sun and earth; to endue with motion that one of 
these bodies which did move, and to fix the limits 
within which the observed changes occurred, both in 
time and distance. 

While the connection between the sun and earth 
was certain, a mutual dependence between the earth 
and the other great source of light, the moon, was 
equally manifest. The invariability in the apparent 
diameter of the moon, demonstrates the fact, that 



INTRODUCTORY LECTURE. 25 

whether the earth were moving or stationary, the 
moon never parts company with our planet. In all 
her wanderings among the fixed stars, in her elonga- 
tions from the sun, in her wondrous phases and 
perpetual changes, some invisible hand held her at 
the same absolute distance from the earth. But to 
decide whether this power resided in the earth or 
the moon, or in both, to explain these wondrous 
changes from the silver crescent of the western sky 
to the full orb which rose with the setting sun, 
pouring a flood of light over all the earth, to develop 
the mysterious connection between the disappear- 
ance of the moon and those terrific phenomena, the 
going out of the sun in dim eclipse — these furnished 
themes for investigation requiring long centuries of 
patient watching, of never ending toil. 

Passing out from the sun and moon to the more 
distant stars, among the brightest of those which 
gemmed the nocturnal heavens, a few were found 
differing from all the rest in the fact that they wan- 
dered from point to point, and at the end of inter- 
vals widely differing among themselves, swept round 
the entire heavens, and returned to their starting 
point, to recommence their ceaseless journies . These 
were named planets, wanderers, in contradistinction 
to the host of stars which were fixed in position, 
unchanged from century to century. 

Hence arose a new and profound series of investi- 
gations: where were these wandering stars urging 
their flight? Were their motions real or apparent? 
Were their distances equal or unequal ? Did any tie 
bind them to the earth, or to the sun, or to each other? 
Were their distances from the earth constant or 
C 



26 STRUCTURE OF THE UNIVERSE. 

variable? Were their motions irregular, or guided 
by law ? Did they accomplish their revolutions among 
the fixed stars in regular curves, or in lawless wan- 
derings? Among all the moving bodies, sun, moon, 
and planets, could any principle of association be 
traced which might bind them together and form them 
into a common system? 

To resolve these profound questions, a critical watch 
is kept on all the moving bodies. Their pathway 
is among the stars, and to these ever during points of 
light their positions are constantly referred. If be- 
yond the limits of the moving bodies a dark veil had 
been drawn so as to have excluded the light of the 
stars, at the first glance it might seem that by such 
a change, simplicity would have been introduced, and 
the perplexity arising from the motion of the planets 
among the profusely scattered stars, would have been 
removed. But let us not judge too hastily. Blot out 
the stars, and give to the sun, moon and planets a 
blank heavens in which to move, and the possibility 
of unraveling their mysterious motions, mutual re- 
lations, and common laws, is gone forever. 

This will become manifest when we reflect that 
on such a change, not a fixed point in all the heavens 
would remain, to which we could refer a moving 
planet. They must then be referred to each other, and 
the motion due to the one, would become inextricably 
involved in that due to the other, and neither could 
be determined with any precision. Like the ocean 
islands which guided the early mariners, so God 
has given to us the stars of heaven as the fixed points 
to which we can ever refer, in all parts of their 



INTRODUCTORY LECTURE. 27 

revolutions, the places of the wandering planets, 
and the swiftly revolving moon. 

As the necessity for accuracy in watching the 
movements of the planets became more apparent, 
the attention was directed to the acquisition of the 
means by which this might be accomplished. Hence 
we find in the earliest ages the astronomer grouping 
the fixed stars into constellations — breaking up the 
great sphere of the heavens into fragments, the more 
easily to study its parts in detail. Not only are the 
stars of each constellation numbered, their brilliancy 
noted, but their relative places in the constellation 
and to each other, are fixed with all the precision 
which the rude means then in use permitted. Names 
are fixed to these different groupings, when or where 
or by whom we know not. Neither history nor tra- 
dition lead us back to this first breaking up of the 
heavens, but the names then bestowed on the fragmen- 
tary parts, the richer constellations, have survived the 
fall of empires, and are fixed forever in the heavens. 

Possessing now a thorough knowledge of the ob- 
jects among which the planets were moving, and the 
means of measuring with approximate accuracy, their 
distance from the stars along their path, it became 
possible to trace a planet in its career, and to note the 
changes of its velocity. New and wonderful discover- 
ies were thus made. It was found that all the planets 
moved with an irregular velocity. Sometimes swiftly 
advancing among the fixed stars, then slowly relaxing 
their speed, they actually stopped, turned backward in 
their career, stopped again, and then, at first slowly 
but afterwards more rapidly, resumed, their onward 
motion. These strange and anomalous motion?, differ- 



28 STRUCTURE OF THE UNIVERSE. 

ing from anything remarked in the sun and moon, 
furnished new themes for discussion, new problems 
for solution. While the phenomena above alluded 
to became known, the same chain of observations 
revealed the remarkable fact, that the periods of 
revolution of the planets, though differing for each 
one of the group, were identical for any one indi- 
vidual, and moreover, that a simple curve marked out 
the pathway of sun, moon and planets, among the 
fixed stars, and that all these wandering bodies were 
confined to a narrow zone or belt in the heavens. 

Centuries had now rolled away, nay, even thou- 
sands of years had slowly glided by, since the mind 
had first given itself to the examination of the heav- 
ens, and while discovery after discovery had reward- 
ed the zeal of the observer in every age, yet the 
grand object of research, the distinction between ac- 
tual and apparent motion, had thus far eluded the 
utmost efforts of human genius. But a brighter day 
was dawning. Each successive effort tore away 
some petty obstruction which impeded the march of 
mind upward towards the lofty region of truth. Facts 
grew and multiplied. Phenomena striking and di- 
versified, were collated and compared. The mind 
in imagination took leave of the earth as the cen- 
tre of all these complex movements, inexplicable on 
its surface, and naturally urged its flight towards 
the sun. There it paused and rested, and from 
this fixed point looked out upon the circling orbs, 
and lo! the complexity of their movements melted 
away. The centre was found — the mystery solved — 
the ponderous earth rescued from its false position, roll- 
ed in its place among the planets, one of the great 



INTRODUCTORY LECTURE. 29 

family that swept in beauty and harmony about their 
common parent the sun. 

The mind now stood upon the first platform of 
the rocky pyramid which it had been slowly rearing 
and with which if had been slowly rising, through long 
centuries of ceaseless toil. One grand point had been 
gained. Darkness had given way to light, but the 
great problem of the universe was yet to be resolved. 
All this long and arduous struggle had only revealed 
what the problem was. Appearances were now 
separated from realities, and with afresh and invigo- 
rated courage the human mind now gives its energies 
to the accomplishment of definite objects, no longer 
working uncertainly in the dark, but with the clear 
light of truth to guide and conduct the investigation. 

Possessed of these extraordinary advantages, the 
advance now became rapid and brilliant, as it had 
previously been slow and discouraging. That the 
planets, reckoning the earth as one, constituted a 
mighty family of worlds, was now manifest — whether 
linked singly to the sun, or mutually influencing each 
other, was the grand question. This great problem 
rested upon the resolution of a multitude of subordi- 
nate ones. The actual curve constituting the plan- 
etary orbits, the magnitude of these orbits, their actual 
position in space, the values and directions of their 
principal lines, the laws of their motion, all these 
and many more questions of equal importance and 
intricacy presented themselves in the outset of the 
examination now fairly commenced. Human skill 
was exhausted in the contrivance and construction 
of mechanical aids by which the movements of the 
planets might be watched with the greater accuracy. 
c2 



30 STRUCTURE OF THE UNIVERSE. 

Partial success crowned these extraordinary efforts, 
but there yet remained delicate investigations which 
with the utmost skill in observing escaped the farthest 
reach of man s eagle gaze, and seemed to bid de- 
fiance to all his powers. 

To conquer these difficulties, one of two things 
must be accomplished : either man must sweep out 
from earth towards the distant planets, to gain a 
nearer and more accurate view, or else bring them 
down from their lofty spheres to subject themselves 
to his scrutinizing gaze. How hopeless the accom- 
plishment of either of these impossible alternatives. 
But who shall prescribe the limits of human genius ? 
In studying the phenomena of the passage of light 
through transparent crystalized bodies, a principle is 
discovered which lets in a gleam of hope on the dis- 
heartened mind. It seizes this principle, converts it to 
its use, and arms itself with an instrument more won- 
derful than any that fancy in its wildest dreams ever 
pictured to the imagination. Yvith the potent aid of 
this magic instrument, the astronomer no longer is 
bound hopelessly to his native earth; without indeed 
quitting in person its surface, his eye gifted with 
superhuman power, ranges the illimitable fields of 
space. He visits the moon, and finds a world with its 
lofty mountains and spreading valleys. The star- 
like planets swell into central worlds, with their cir- 
cling moons, and myriads of fixed stars, hitherto be- 
yond the reach of human vision, stand revealed in all 
their sparkling beauty. It is as if the united ranges 
of a thousand eyes were all concentrated in a single 
one. 

A new era now dawns on the world. The delicate 



INTRODUCTORY LECTURE. 31 

and invisible irregularities of the planetary motions 
are now fully revealed, and the data rapidly accumu- 
late by means of which the last grand question is 
to be resolved. The orbitual curves are determined. 
The laws of the revolving planets are revealed. A 
mysterious relation between the distances of the 
planets from the sun and their periods of revolution 
unites them positively into one grand family group. 
That they are bound to the sun by some inscrutable 
power, is certain, and it now remains to determine 
the law of increase and decrease of this force for all 
possible distances. This last truth is finally achieved, 
and the wisdom of God is vindicated in the beautiful 
structure of our grand system. 

The second lofty platform is reached in the mighty 
pyramid, whose summit is now nearing the stars of 
heaven. From this elevation the mind looks out 
upon the circling planets and their revolving satellites, 
and the mysterious comet, and ventures to propound 
the question, do these bodies so interfere with the 
movements of each other, as to affect permanently 
the structure by which the equilibrium and stability of 
the entire system is guarantied ? 

To answer this question, a new train of investiga- 
tion is commenced, satellite is weighed against 
planet, and planet against the sun, until the mass 
of matter contained in each individual of the system 
becomes accurately known. Then is undertaken the 
grand problem of perturbations. The telescope re- 
veals the fact that slow and mysterious changes are 
going on in the mean motions of the moon, in the 
figure of the planetary orbits, and in the relative po- 
sitions which these orbits hold to each other. Are 



32 STRUCTURE OF THE UNIVERSE. 

these changes ever progressive ? If this be true, then, 
does the system contain within itself the seeds of de- 
cay, the elements of its own destruction. Slowly but 
surely as the solemn tread of time, the end must come, 
and one by one planet and satellite and comet, sink 
forever in the sun. Long and arduous was the strug- 
gle to reach the true answer to this difficult question. 
The entire solution involved a multitude of parts. 

When the mutual dependence of the multitude of 
bodies constituting our system was discovered, when 
planet, and satellite, and comet, were found to feel 
and sway to the influence which each exerted on the 
other, the simplicity of their movements was gone for 
ever ; orbits once fixed in the heavens, slowly swung 
away from their moorings ; the beautiful precision 
which had to all appearance marked the planetary 
curves, was destroyed. The regularity of their motions 
was changed into irregularity, and a system of com- 
plexity which seemed to bid defiance to all effort at 
comprehension, presented itself to the human intellect. 

It was no less than this — given, a system of revolv- 
ing worlds, mutually operating on each other ; re- 
quired, their magnitudes, masses, distances, motions, 
and positions, at the close of a thousand revolutions. 
What mind possessed the gigantic power to grasp 
this mighty problem ? Reason was lost in wander- 
ing mazes, and the brightest intellect sunk clouded 
in gloom. 

In this dilemma, the mind turns inward on its own 
resources. As the physical man climbs some moun- 
tain height by successive efforts, rising higher and 
higher, scaling rock after rock, and mounting precipice 
after precipice, by the use of strength comparatively 



INTRODUCTORY LECTURE. 33 

feeble, resting and recruiting as it becomes exhausted, 
was it impossible, to contrive some mental machinery 
which might give to the reason the power of pros- 
ecuting its difficult researches, in such manner that 
it might stop and rest, and not lose what it had 
already gained in its onward movement ? 

Geometry had invigorated the reason, as exercise 
toughens and strengthens the muscles of the human 
frame. But it had given to the mind no mechanical 
power, wherewith to conquer the difficulties which 
rose superior to its natural strength. Archimides 
wanted but a place whereon to stand, and with his 
potent lever he would lift the world. The astronomer 
demands an analogous mental machinery to trace 
out the complex wanderings of a system of worlds. 
What the human mind demands and resolves to find, 
it never fails to discover. The infinitesimal analysis is 
reached, its principles developed, its resistless power, 
compelled into the service of human reason. I shall 
not now stop to explain the nature of this analysis. 
Its power and capacity alone engage our attention at 
the present. Once having seized on a wandering 
planet, it never relaxes its hold, no matter how com- 
plicated its movements, how various the influences to 
which it may be subjected, how numerous its revolu- 
tions, no escape is possible. This subtle analysis 
clings to its object, tracing its path and fixing its place 
with equal ease, at the beginning, middle, or close of 
a thousand revolutions, though each of these should 
require a century for its accomplishment. 

Armed with this analysis, which the mind had crea- 
ted for its use, giving to it a strength only commensu- 
rate with the increased power which had been given 



34 STRUCTURE OF THE UNIVERSE. 

to the human eye, it concentrated its energies once 
more upon this last greatest problem. One by one 
these strong holds give way, the resistless power of 
analysis marches onward from victory to victory, until 
finally the sublime result is reached, the system is 
stable, the equilibrium is perfect ; slowly rocking to 
and fro in periods which stun the imagination, the 
limits are prescribed beyond which these fluctua- 
tions shall never pass. 

Here it would seem that human ambition might, 
rest. Satisfied with having mastered the mysteries of 
the system with which we are united, the mind might 
cease its arduous struggle, and leave the wilderness of 
fixed stars free from its intrusions and ceaseless per- 
secutions. But this is not the effect produced by vic- 
tory ; success but engenders new desires, and prompts 
to more difficult enterprises. Man having obtained 
the mastery over his own system, boldly wings his 
flight to the star-lit vault, and resolves to number its 
countless millions, to circumscribe its limitless extent, 
to fathom its infinite depth, to fix the centre about 
which this innumerable host is wheeling its silent and 
mysterious round. 

Here commences a new era. The first step in the 
stupendous enterprise is to determine the distance of 
some one fixed star. Here again the mind is long 
left to struggle with difficulties which it seemed that 
no ingenuity or skill could remove. But its efforts do 
not go unrewarded. If it fails in the accomplishment 
of its grand object, it is rewarded by the most brilliant 
discoveries. The mighty law governing the planetary 
worlds is extended to the region of the fixed stars, mo- 
tion is there detected, orbitual motion, the revolution of 



INTRODUCTORY LECTURE. 35 

sun about sun. The swift velocity of light is measured, 
to become the future unit in the expression of the mighty 
distances which remain yet to be revealed. Ever baf- 
fled but never conquered, the mind returns again and 
again to the attack, till finally the problem slowly 
yields, the immeasurable gulf is passed, and the dis- 
tance of a single star rewards the toils of half a cen- 
tury. But what a triumph is this ? It is no less than 
a revelation of the scale on which the universe is built. 
The interval from sun to fixed stars, is that by which 
the stars are separated; and a reach of distance is 
opened up to the mind, which it only learns to con- 
template by long continued effort. 

But another startling fact is revealed in the prose- 
cution of these profound investigations. The minute 
examinations of the fixed stars, have changed their 
character. For thousands of years they had been re- 
garded as absolutely fixed among each other. This 
proves to be mere illusion, resulting from the use of 
means inadequate for the determination of their min- 
ute changes. Under the scrutinizing gaze of the eye, 
with its power increased a thousand fold, the millions 
of shining orbs which fill the heavens, are all found to 
be slowly moving around each other, slowly as seen 
from our remote position, but with amazing velocity 
when examined near at hand. 

A new problem of surprising grandeur now pre- 
sents itself. Are these motions real ? or are they due 
to a motion in the great centre of our system ? A se- 
ries of examinations analogous to those which divided 
between the real and apparent motions in the planets, 
is commenced and prosecuted with a zeal and devotion 
unsurpassed in the history of science. The mind rises 



36 STRUCTURE OF THE UNIVERSE. 

to meet the sublime investigation. For a hundred 
years it toils on; again it triumphs; the truth is reveal- 
ed. The immobility of the sun is gone forever ; our 
last fixed point is swept from under us, and now the 
entire universe is in motion. 

With redoubled energy the mind still prosecutes the 
inquiry, whither is the sun sweeping, and with what 
velocity does it pursue its unknown path ? Strange 
and incredible as it may appear, these questions are 
answered; and in attaining this answer, the means are 
reached to separate between the real and apparent 
motions of the fixed stars, and to study their complex 
changes, and to rise by slow degrees, to a complete 
knowledge of the movements of the grand sidereal sys- 
tem. Here we pause. Rapidly have we descended the 
current of astronomical research, we have attained the 
boundary of the known. We stand on the dim confines 
of the unknown. All behind us is clear and bright and 
perfect, all before us is shrouded in gloom and dark- 
ness and doubt. Yet the twilight of the known flings 
its feeble light into the domain of the unknown, and 
we are permitted to gather some idea, not of all that 
remains to be done, but of that which must be first ac- 
complished. 

Let us then stretch forward and propound some of 
those questions which nature yet presents for solution, 
but which have hitherto resisted the efforts of the hu- 
man mind. First of all, we begin with our own sys- 
tem. How came it to be constituted as it actually 
exists ? All the analogies of nature forbid the idea 
that it was thus instantly called into being by the 
fiat of Omnipotence. Does it come, then, from some 
primitive modification of matter, under the action of 



INTRODUCTORY LECTURE. 37 

laws working out their results in countless millions of 
ages ? Who shall present the true cosmogony of the 
solar system. 

But this is only one unit among many millions. 
Whence the myriads of stars ? those stupendous ag- 
gregations into mighty clusters ? what the laws of their 
wonderful movements, of their perpetual stability ? 
Who will explain the periodical stars, that wax and 
wane, like the changing moon : or still more wonder- 
ful, reveal the mystery of those which have suddenly 
burst on the astonished vision of man, and have as 
suddenly gone out forever in utter darkness. 

Such are the questions which remain for the reso- 
lution of future ages. We may not live to witness 
these anticipated triumphs of mind over matter ; but 
who can doubt the final result? Look backward to 
the Chaldean shepherd, who watched the changing 
moon from the plains of Shinar, and wondering, 
asked if future generations would reveal those mys- 
terious phases ? Compare his mind and knowledge 
with those of the modern astronomer, who grasps 
at a single glance, the past, present, and future 
changes of an entire system. Are the heights which 
remain to be reached, more rugged, more inaccessible } 
than those which have been already so triumphantly 
scaled ? The observations recorded in Babylon three 
thousand years ago, have reached down through the 
long series of centuries, and are of inestimable value, 
in the solution of some of the darkest problems with 
which the mind has ever grappled. In like manner, 
the records we are now making, shall descend to un- 
born generations, and contribute to effect the triumphs 
of genius when three thousand years shall have rolled 
D 



ofl STRUCTURE OF THE UNIVERSE. 

away. If doubt arises as to the final resolution of 
these profound questions, from the immense distance 
of the objects under examination, let us call to mind 
the fact, that the artificial eye which man has fur- 
nished for his use, possesses a glance so piercing, 
that no distance can hide an object from his searching 
vision. 

Should Sirius, to escape this fiery glance, dart 
away from its sphere, and wing its flight at a velocity 
of twelve millions of miles in every minute, for a 
thousand years; nay, should it sweep onward at the 
same speed for ten thousand years, this stupendous 
distance cannot bury it from the persecuting gaze of 
man. But if distance is to form no barrier, no termi- 
nus to these investigations, surely there is one element 
which no human ingenuity can overcome. The com- 
plex movements of the planetary orbs have been 
revealed, because they have been repeated a thousand 
times under the eye of man, and from a comparison 
of many revolutions, the truth has been evolved. 
But tens of thousands of years must roll away before 
the most swiftly moving of all the fixed stars shall 
complete even a small fragment of its mighty orbit. 
With motions thus shrouded, these would seem to be in 
entire security from the inquisitive research of a being 
whose whole sweep of existence is but a moment, 
when compared with these vast periods. But let us not 
judge too hastily. The same piercing vision that fol- 
lows the retreating star to depths of space almost infi- 
nite, is armed with a power so great, that if this same 
star should commence to revolve around some grand 
centre, and move so slowly that five millions of years 
must roll away before it can complete one circuit, not 



INTRODUCTORY LECTURE. 39 

even a single year shall pass before its motion shall be 
detected, in ten years its velocity shall be revealed, 
and in the life time of a single observer its mighty 
period shall become known. 

If human genius is not to be baffled either by dis- 
tance or time, numbers shall overwhelm it, and the 
stars shall find their safety in their innumerable mil- 
lions. This retreat may even fail. The watch-towers 
of science now cover the whole earth, and the senti- 
nels never sleep. No star or cluster or constellation, 
can ever set. It escapes the scrutinizing gaze of one 
astronomer, to meet the equally piercing glance of 
another. East and west, and north and south, from 
the watch towers of the four quarters of the globe, 
peals the solemn mandate, onward ! 

Here we pause. We have closed the enunciation of 
the great problem whose discussion and solution lie 
before us, a problem whose solution has been in pro- 
gress six thousand years — one which has furnished to 
man the opportunities of his loftiest triumphs, one 
which has taxed in every age the most vigorous efforts 
of human genius, a problem whose successive develop- 
ments have demonstrated the immortality of mind, 
and whose sublime results have vindicated the wisdom 
and have declared the glory of God. You have 
listened to the enunciation, we now invite you to fol- 
low us in the demonstration. And may that Almighty 
power, which built the heavens, give to me wisdom to 
reveal, and to you power to grasp the truths and doc- 
trines, wrested by mind from nature in its long strug- 
gle of sixty centuries of toil ! 



LECTURE II. 

THE DISCOVERIES OF THE PRIMITIVE AGES. 

To those who have given but little attention to the 
science of astronomy, its truths, its predictions, its rev- 
elations, are astonishing ; and but for their rigorous 
verification, would be absolutely incredible. When 
we look out upon the multitude of stars which adorn 
the nocturnal heavens, scattered in bright profusion 
in all directions, without law, and regardless of order 
— when with telescopic aid, thousands are increased 
to millions, and suns and systems and universes, rise 
in sublime perspective, as the visual ray sweeps out- 
ward to distances which defy the powers of arithme- 
tic to express, how utterly futile does it seem, for the 
mind to dare, to pierce and penetrate, to number, 
weigh, measure and circumscribe, these innumerable 
millions ? It is only when we remember, that from 
the very cradle of our race, strong and powerful 
minds, have in rapid and continuous succession, bent 
their energies upon the solution of this grand problem, 
that we can comprehend, how it is, that light now 
breaks in upon us, from the very confines of the 
universe, dimly revealing the mysterious forms, which 
lie yet half concealed in the unfathomable gulfs of 
space. When I reflect on the recent triumphs of 
human genius — when I stand on the shore of that 
d2 (41) 



42 STRUCTURE OF THE UNIVERSE. 

mighty stream of discovery, which has grown broader 
and deeper, as successive centuries have rolled away, 
gathering in strength and intensity, until it has em- 
braced the whole universe of God ; I am carried back- 
ward through thousands of years, following this stream, 
as it contracts towards its source, till finally its silver 
thread is lost in the clouds and mists of antiquity. I 
would fain stand at the very source of discovery, and 
commune with that unknown god-like mind which 
first conceived the grand thought, that even these 
mysterious stars might be read, and that the bright 
page which was nightly unfolded to the vision of man, 
needed no interpreter of its solemn beauties, but 
human genius. There is to my mind, no finer speci- 
men of moral grandeur, than that presented by him 
who first resolved to read and comprehend the heav- 
ens. On some lofty peak he stood, in the stillness of 
the midnight hour, with the listening stars as wit- 
nesses of his vows, and there, conscious of his high 
destiny, and of that of his race, resolves to commence 
the work of ages. " Here," he exclaims, " is my 
watch-tower, and yonder bright orbs, are henceforth 
my solitary companions. Night after night, year 
after year, will I watch and wait, ponder and reflect, 
until some ray shall pierce the deep gloom which now 
wraps the world." 

Thus resolved the unknown founder of the science 
of the stars. His name and his country are lost 
forever. What matters this, since his works, his dis- 
coveries, have endured for thousands of years, and 
will endure,- as long as the moon shall continue to fill 
her silver horn, and the planets to roll and shine. 

Go with me, then, in imagination, and let us stand 



DISCOVERIES OF THE PRIMITIVE AGES. 43 

beside this primitive observer, at the close of his 
career of nearly a thousand years, (for we must pass 
beyond the epoch of the deluge, and seek our first 
discoveries among those sages, whom, for their vir- 
tues, God permitted to count their age, not by years, 
but by centuries,) and here we shall learn the order 
in which the secrets of the starry world slowly 
yielded themselves, to long and persevering scrutiny. 
And now let me unfold, in plain and simple lan- 
guage, the train of thought, of reasoning and research, 
which marked this primitive era of astronomical 
science. It is true that history yields no light, and 
tradition even fails, but such is the beautiful order in 
.the golden chain of discovery, that the bright links 
which are known, reveal with certainty, those which 
are buried in the voiceless past. — If then it were 
possible to read the records of the founder of astrono- 
my, graven on some column of granite, dug from the 
earth, whither it had been borne by the fury of the del- 
uge, we know now what its hieroglyphics would re- 
veal, with a certainty scarcely less than that which 
would be given by an actual discovery, such as we have 
imagined. We are certain that the first discovery 
ever recorded, as the result of human observation, was 
on the moon. 

The sun, the moon, the stars, had long continued to 
rise, and climb the heavens, and slowly sink beneath 
the western horizon. The spectacle of day and night, 
was then as now, familiar to every eye ; but in gazing 
there was no observation, and in mute wonder there 
was no science. When the solitary observer took his 
post, it was to watch the moon. Her extraordinary 
phases had long fixed his attention. Whence came 



44 STRUCTURE OF THE UNIVERSE. 

these changes ? The sun was ever round and brilliant 
— the stars shone with undimmed splendor — while 
the moon was ever waxing and waning, sometimes 
a silver crescent hanging in the western sky, or full 
orbed, walking in majesty among the stars, and 
eclipsing their radiance, with her overwhelming splen- 
dor. Scarcely had the second observation been made 
upon the moon, when the observer was struck with 
the wonderful fact, that she had left her place among 
the fixed stars, which on the preceding night he had 
accurately marked. Astonished, he again fixes her 
place by certain bright stars close to her position, and 
waits the coming of the following night. His suspi- 
cions are confirmed — the moon is moving; and what 
to him is far more wonderful, her motion is precisely 
contrary to the general revolution of the heavens, from 
east to west. With a curiosity deeply aroused, he 
watches from night to night, to learn, whether she 
will return upon her track; but she marches steadily 
onward among the stars, until she sweeps the entire 
circuit of the heavens, and returns to the point first 
occupied, to recommence her ceaseless cycles. 

An inquiry now arose, whether the changes in the 
moon, her increase and decrease, could in any way 
depend on her place among the fixed stars. To 
solve this question, required a longer period. The 
group of stars among which the new moon was first 
seen was accurately noted, so as to be recognized at 
the following new moon, and doubtless our primitive 
astronomer hoped to find that in this same group 
the silver crescent, when it should next appear, would 
be found. But in this he was disappointed; for when 
the moon became first faintly visible in the western 



DISCOVERIES OF THE PRIMITIVE AGES. 45 

sky, the group of stars which had ushered her in be- 
fore, had disappeared below the horizon, and a new 
group had taken its place ; and thus it was discovered 
that each successive new moon fell farther and farther 
backward among the stars. By counting the days 
from new moon to new moon, and those which elaps- 
ed whije the moon was passing round the heavens 
from a certain fixed star to this same star again, it 
was found, that these two periods were different; the 
revolution from new to new occupying 29£ days, 
while the sidereal revolution, from star to star, re- 
quired 27^ days. 

This backward motion of the moon among the stars, 
must have perplexed the early astronomers ; and for 
a long while it was utterly impossible to decide 
whether the motion was real or only apparent — anal- 
ogy would lead to the conclusion that all motion must 
be in the same direction, and as the heavens revolved 
from east to west, it seemed impossible that the moon, 
which manifestly participated in this general move- 
ment, should have another and a different motion, 
from west to east. There was one solution of this 
mystery, and I have no doubt it was for a long while 
accepted and believed. It was this. By giving to 
the moon a slower motion from east to west, than the 
general motion of the heavens, she would appear to 
lag behind the stars, which would by their swifter ve- 
locity pass by her, and thus occasion in her the ob- 
served apparent motion, from west to east. We shall 
see presently how this error was detected. 

The long and accurate vigils of the moon, and the 
necessity of recognizing her place, by the clusters or 
groups of stars among which she was nightly found, 



46 STRUCTURE OF THE UNIVERSE. 

had already familiarized the eye with those along her 
track, and even thus early the heavens began to be di- 
vided into constellations. The eye was not long in 
detecting the singular fact, that this stream of constel- 
lations, lying along the moon's path, was constantly 
flowing to the west, and one group after another ap- 
parently dropping into the sun, or at least becoming 
invisible, in consequence of their proximity to this 
brilliant orb. A closer examination revealed the fact, 
that the aspect of the whole heavens was changing 
from month to month. Constellations which had been 
conspicuous in the west, and whose brighter stars 
were the first to appear as the twilight faded, were 
found to sink lower and lower towards the horizon, till 
they were no longer seen ; while new groups were 
constantly appearing in the east. 

These wonderful changes, so strange and inexpli- 
cable, must have long perplexed the early student of 
the heavens. Hitherto the stars, along the moon's 
route, had engaged special attention ; but at length 
certain bright and conspicuous constellations, towards 
the north, arrested the eye: and these were watched to 
see whether they would disappear. — Some were found 
to dip below the western horizon, soon to re-appear 
in the east ; while others revolving with the general 
heavens, rose high above the horizon, swept steadily 
round, sunk far down, but never disappeared from the 
sight. This remarkable discovery soon led to another 
equally important. In watching the stars in the north 
through an entire night, they all seemed to describe 
circles ; having a common centre, these circles grew 
smaller and smaller as the stars approached nearer 1o 
the centre of revolution, until finally one bright star 



DISCOVERIES OF THT PRIMITIVE AGES. 47 

was found, whose position was ever fixed.— Alone un- 
changed while all else was slowly moving. The dis- 
covery of this remarkable star, must have been hailed 
with uncommon delight by the primitive observer of 
the heavens. If his deep devotion to the study of the 
skies, had created surprise among his rude country- 
men, when he came to point them to this never chang- 
ing light hung up in the heavens, and explained its uses 
in guiding their wanderings on the earth, their sur- 
prise must have given place to admiration. Here was 
the first valuable gift of primitive astronomical science 
to man. 

But to the astronomer this discovery opened up a 
new field of investigation, and light began to dawn 
on some of the most mysterious questions which had 
long perplexed him. He had watched the constella- 
tions near the moon's track slowly disappear in the ef- 
fulgence of the sun, and when they were next seen, it 
was in the east, in the early dawn, apparently emerg- 
ing from the solar beams, having actually passed by 
the sun. Watching and reflecting, steadily pursuing the 
march of the northern constellations, which never en- 
tirely disappeared, and noting the relative positions 
of these, and those falling into the sun, it was at last 
discovered that the entire starry heavens was slowly 
moving forward to meet and pass by the sun, or else 
the sun itself was actually moving backward among 
the stars. This apparent motion had already been 
detected in the moon, and now came the reward of 
long and diligent perseverance. The grand discovery 
was made, that both the sun and moon were moving 
among the fixed stars, not apparently, but absolutely. 
The previously received explanation of the moon's 



48 STRUCTURE OF THE UNIVERSE. 

motion, could no longer be sustained; for the starry 
heavens could not at the same time so move as to pass 
by the moon in one month, and to pass by the sun in a 
period twelve times as great. A train of the most im- 
portant conclusions flowed at once from this great dis- 
covery. — The starry heavens passed beneath and 
around the earth, — the sun and moon were wandering 
in the same direction, but with different velocities 
among the stars, — the constellations actually filled the 
entire heavens above the earth and beneath the earth, 
— the stars were invisible in the day time, not because 
they did not exist, but because their feeble light was lost 
in the superior brilliancy of the sun. The heavens were 
spherical, and encompassed like a shell the entire earth, 
and hence it was conceived that the earth itself was 
also a globe, occupying the centre of the starry sphere. 

It is impossible for us, familiar as we are at this day 
with these important truths, to appreciate the rare merit 
of him who by the power of his genius, first rose to their 
knowledge and revealed them to an astonished world. 
We delight to honor the names of Kepler, of Galileo, 
of Newton; but here are discoveries so far back in the 
dim past, that all trace of their origin is lost, which 
vie in interest and importance with the proudest 
achievements of any age. 

With a knowledge of the sphericity of the heavens, 
the revolution of the sun and moon, the constellations 
of the celestial sphere, the axis of its diurnal revolu- 
tion, astronomy began to be a science, and its future 
progress was destined to be rapid and brilliant. A line 
drawn from the earth's centre to the north star formed 
the axis of the heavens, and day and night around 
this axis all the celestial host were noiselessly pursuing 



DISCOVERIES OF THE PRIMITIVE AGES. 49 

their never ending journies. — Thus far, the only mov- 
ing bodies known, were the sun and moon. These 
large and brilliant bodies, by their magnitude and 
splendor, stood out conspicuously, from among the 
multitude of stars, leaving these minute but beautiful 
points of light, in one great class, unchangeable among 
themselves, fixed in their groupings and configura- 
tions, furnishing admirable points of reference, in 
watching and tracing out the wanderings of the sun 
and moon. 

To follow the moon as she pursued her journey 
among the stars was not difficult ; but to trace the 
sun in his slower and more majestic motion, and to 
mark accurately his track, from star to star, as he 
heaved upward to meet the coming constellations, 
was not so readily accomplished. Night after night, 
as he sunk below the horizon, the attentive watcher 
marked the bright stars near the point of setting which 
first appeared in the evening twilight. — These grad- 
ually sunk towards the sun on successive nights, and 
thus was he traced from constellation to constellation, 
until the entire circuit of the heavens was performed, 
and he was once more attended by the same bright 
stars, that had watched long before, his sinking in the 
west. Here was revealed the measure of the Year. 
The earth had been verdant with the beauties of 
spring, — glowing with the maturity of summer, — rich 
in the fruits of autumn, — and locked in the icy chains 
of winter, while the sun had circled round the heavens. 
His entrance into certain constellations marked the 
coming seasons, and man was beginning to couple 
his cycle of pursuits on earth with the revolutions of 
the celestial orbs. 
E 



50 STRUCTURE OF THE UNIVERSE. 

While intently engaged in watching the sun as it 
slowly heaved up to meet the constellations, some ar- 
dent devotee to this infant science, at length marked 
in the early twilight a certain brilliant star closely at- 
tendant upon the sun. The relative position of these 
two objects was noted, for a few consecutive nights, 
when with a degree of astonishment, of which we can 
form no conception, he discovered that this brilliant 
star was rapidly approaching the sun, and actually 
changing its place among the neighboring stars, — 
night after night he gazes on this unprecedented phe- 
nomenon, a moving star ! and on each successive night 
he finds the wanderer coming nearer and nearer to 
the sun. At last it disappears from sight, plunged in 
the beams of the upheaving sun. What had become 
of this strange wanderer ? was it lost forever ? were 
questions which were easier asked than answered. — 
But patient watching had revealed the fact, that when 
a group of stars, absorbed into the sun's rays, disap- 
peared in the west, they were next seen in the eastern 
sky, slowly emerging from his morning beams. Might 
it not be possible, that this wandering star would pass 
by the sun, and re-appear in the east? With how much 
anxiety must this primitive discoverer have watched in 
the morning twilight ? Day after day he sought his 
solitary post, and marked the rising stars, slowly lift- 
ing themselves above the eastern horizon. The gray 
dawn came, and the sun shot forth a flood of light, the 
stars faded and disappeared, and the watcher gives 
over, till the coming morning. But his hopes are 
crowned at last. Just before the sun breaks above 
the horizon, in the rosy east, refulgent with the com- 
ing day, he descries the pure white silver ray of his 



DISCOVERIES OF THE PRIMITIVE AGES. 51 

long lost wanderer. It has passed the sun, — it rises in 
the east, — the first planeTii discovered ! 

With how much anxiety and interest did the delighted 
discoverer trace the movements of his wandering star. 
Here was a new theme for thought, for observation, for 
investigation; would this first planet sweep round the 
heavens, as did the sun and moon ? would it always 
move in the same direction ? would its path lie among 
those groups of stars among which the sun and moon 
held their course ? Encouraged by past success, he 
rejoicingly enters on the investigations of these ques- 
tions. For some time the planet pursues its journey 
from the sun, leaving it farther and farther behind. 
But directly it slackens its pace, — it actually stops in 
its career, and the astonished observer, perhaps thinks 
that his wandering star had again become fixed. Not 
so, — a few days of watching dispels this idea. Slowly 
at first, and soon more swiftly, the planet seeks again 
the sun, moving backwards on its former path, until 
finally its light is but just visible in the east at early 
dawn. Again it is lost in the sun's beams for a 
time, and contrary to all preceding analogy, when 
next seen, its silver ray comes out pure and bright, 
just above the setting sun. It now recedes from the 
sun, on each successive evening increasing its dis- 
tance, till it again reaches a point never to be passed 
— here it stops — is stationary for a day or two, and 
then again sinks downward to meet the sun. How 
wonderful and inexplicable the movements of this 
wandering star must have appeared in the early ages ! 
oscillating backward and forward, never passing its 
prescribed limits, and ever closely attendant upon the 
sun. Where the sun sunk to repose, there did the 



52 STRUCTURE OF THE UNIVERSE. 

faithful planet sink, and where the sun rose, at the 
same point did the wandering star make its appear- 
ance. The number of days was accurately noted, 
from the stationary point in the east above the sun, to 
the stationary point in the west above the sun, and 
thus the period, 584 days, from station to station, be- 
came known. 

The discovery of one planet, led the way to the 
rapid discovery of several others. If we may judge 
of their order by their brilliancy, Jupiter was the se- 
cond wanderer revealed among the stars. Then fol- 
lowed Mars, and Saturn, and after a long interval 
Mercury was detected, hovering near the sun, and im- 
itating the curious motions of Venus. 

Here the progress of planetary discovery was sud- 
denly arrested, keen as was the vision of the old astron- 
omer, long and patient as was his scrutiny, no depth 
of penetration of unaided vision could stretch beyond 
the mighty orbit of Saturn, and the search was given 
over. — A close examination of the planets revealed 
many important facts. Three of them, Mars, Jupiter, 
and Saturn, were found to perform the circuit of the 
heavens, like the sun and moon, and in the same di- 
rection; with this remarkable difference, that while the 
sun and moon, moved steadily and uniformly in the 
same direction, the planets occasionally slackened 
their pace, would then stop, move backwards on their 
track, stop again, and finally resume their onward 
motion. Their periods of revolution were discovered 
by marking the time which elapsed, after setting out 
from some brilliant and well known fixed star, until 
they should perform the entire circuit of the heavens 
and once more return to the same star. The times of 



DISCOVERIES OF THE PRIMITIVE AGES. 53 

revolution were found to differ widely from each 
other ; Mars requiring about 687 days, Jupiter 4,332 
days, and Saturn 10,759 days, or nearly thirty of our 
years. 

The planets all pursued their journies in the heav- 
ens, among the same constellations which marked the 
paths of the sun and moon, and hence these groups of 
stars concentrated the greatest amount of attention 
among the early astronomers, and became distin- 
guished from all the others. 

Whatever light may be shed upon antiquity by 
deciphering the hieroglyphic memorials of the past, 
there is no hope of ever going far enough back, to 
reach even the nation, to which we are indebted for 
the first rudiments of the science of the stars. 

Thus far in the prosecution of the study of the 
heavens, the eye and the intellect had accomplished 
the entire work. Rapidly as we have sketched the 
progress of early discovery, and short as may have 
been the period in which it was accomplished, no one 
can fail to perceive, how vast is the difference be- 
tween the light that thus early broke in upon the 
mind, heralding the coming of a brighter day, and 
the deep and universal darkness which had covered 
the world, before the dawn of science. Encouraged 
by the success which had thus far rewarded patient 
toil, the mind of man pushes on its investigations 
deeper and deeper into the domain of the mysterious 
and unknown. 

In watching the annual revolution of the sun among 

the fixed stars, one remarkable peculiarity had long 

been recognized. While the interval of time, from the 

rising to the setting of the stars, was ever the same 

e2 



54 DISCOVERIES OF THE PRIMITIVE AGES. 

at all seasons of the year, the interval from the rising 
to the setting of the sun, was perpetually changing, 
passing through a cycle which required exactly one 
year for its completion. It became manifest that 
the sun did not prosecute its annual journey among 
the stars, in a circle parallel with those described by 
the stars, in their diurnal revolution. His path was 
oblique to those circles, and while he participated in 
their diurnal motion, he was sweeping by his annual 
revolution round the heavens, and was at the same 
time, by another most extraordinary movement, car- 
ried towards the north to a certain distance, then 
stopping, commenced a return towards the south, — 
reached his southern limit, — again changed his direc- 
tion, and thus oscillated from one side to the other of 
his mean position. 

These wonderful changes became the objects of 
earnest investigation. In what curve did the sun 
travel among the stars? All diurnal motion was per- 
formed in a circle, the first discovered, the simplest 
and the most beautiful of curves : and in this curve, 
analogy taught the early astronomers, that all celestial 
movements must be performed. It became there- 
fore, a matter of deep interest, to trace the sun's path 
accurately among the stars, to mark his track, and 
to see whether it would not prove to be a circle. 
To accomplish this, more accurate means must be 
adopted, than the mere watching of the stars which 
attended the rising or setting sun. The increase 
and decrease of the shadow of some high pointed 
rock, to whose refreshing shade the shepherd astrono- 
mer had repaired in the heat of noon, and beneath 
which he had long pondered this important problem, 



STRUCTURE OF THE UNIVERSE. 55 

first suggested the means of its resolution. — As the 
summer came on, he remarked that the length of 
the noon shadow of his rock, perpetually decreased 
from day to day. As the sun became more nearly 
vertical at noon, the shadow gave him less and 
less shelter. Watching these noon shadows, from 
day to day, he found them proportioned to the sun's 
northern or southern motion, and finally the thought 
entered his mind, that these shadows would mark 
with certainty, the limits of the sun's motion north 
and south, — the character of his orbit or route among 
the stars, — the changes and duration of the seasons, 
and the actual length of the year, which thus far had 
been but roughly determined. To accomplish the ob- 
servations more accurately, an area on the ground 
was smoothed and leveled, and in its centre a verti- 
cal pole was erected some ten or fifteen feet in length, 
whose sharp vertex cast a well defined shadow. 
And here we have the first astronomical instrument, 
the gnomon, ever devised by the ingenuity of man. 
Simple as it is, by its aid the most valuable results 
were obtained. 

The great point was to mark with accuracy the 
length of the noon-day shadow, from month to month, 
throughout the entire year. Four remarkable points 
in the sun's annual track, were very soon detected 
and marked. One of these occurred in the summer, 
and was that point occupied by the sun on the 
day of the shortest noon shadow. Here the sun 
had reached his greatest northern point, and for a 
few days the noon shadow, cast by the gnomon, 
appeared to remain the same, and the sun stood 
still. The noon shadows now increased slowly, for 



56 DISCOVERIES OF THE PRIMITIVE AGES. 

six months, as the sun moved south, till a second 
point was noted, when the noon shadow had reached 
its greatest length. Again it became stationary, and 
again the sun paused and stood still, before com- 
mencing his return towards the north. These points 
w T ere called the summer and winter solstices, and oc- 
curred at intervals of half a year. At the summer 
solstice, the longest day occurred, while at the winter 
solstice, the shortest day was always observed. These 
extreme differences between the length of the day 
and night, occasioned the determination of the other 
two points. From the winter solstice, the noon 
shadows decreased as the length of the day increased, 
until finally the day and night were remarked to be 
of equal length, and the distance to which the shadow 
of the gnomon was thrown on that day, was ac- 
curately fixed. If on this day the diurnal circle des- 
cribed by the sun, could have been marked in the 
heavens by a circle of light, sweeping from the east 
to the west, so that the eye might rest upon and 
retain it, and if at the same time the sun's annual 
path among the fixed stars could have been equally 
exhibited in the heavens, by a circle of light, these 
two circles would have been seen to cross each other, 
and at their point of crossing, the sun would have 
been found. The diurnal circle was called the equa- 
tor, the sun's path the ecliptic, and the point of in- 
tersection was called appropriately, the equinox. — 
As the sun crossed the equator in the spring and 
autumn, these points received the names of the vernal 
and autumnal equinoxes, and were marked with all 
the precision which the rude means then in use 
rendered practicable. 



DISCOVERIES OF THE PRIMITIVE AGES. 57 

The bright circle already imagined in the heavens 
to represent the sun's annual track among the stars, 
passed obliquely across the equator, and the amount 
by which these circles were inclined to each other was 
actually measured in these early ages, with no mean 
precision by the noon shadows of the gnomon. The 
ray casting the shortest noon shadow, was inclined to 
the ray forming the longest noon shadow, under an 
angle precisely double of the inclination of the eclip- 
tic or sun's path to the equator, and the inclination of 
these two rays marked exactly the annual motion of 
the sun from south to north, or from north to south. 
A close examination of the order of increase and de- 
crease in the length of the noon shadows cast by the 
gnomon, demonstrated the important truth already 
suspected, that the sun's path was actually a circle, 
but inclined, as has already been shown, to the diur- 
nal circles of the stars and to the equator. 

By counting the days which elapsed from the sum- 
mer solstice to the summer solstice again, a knowl- 
edge of the length of the year, or period of the sun's 
revolution, was obtained. But here again a discov- 
ery was made which produced an embarrassment to 
the early astronomer, which all their perseverance and 
research never succeeded in removing. 

In these primitive ages the heavenly bodies were 
regarded with feelings little less than the reverence 
we now bestow on the Supreme Creator. The sun es- 
pecially, as the Lord of life and light, was regarded 
with feelings nearly approaching to adoration, even 
by the astronomers themselves. The idea early be- 
came fixed, that the chief of the celestial bodies must- 
move with a uniform velocity in a circular orbit, never 



58 STRUCTURE OF THE UNIVERSE. 

increasing or decreasing. Change being inconsistent 
with the supreme and dignified station which was as- 
signed to him— what then must have been the aston- 
ishment of the primitive astronomers, who in counting 
the days from the summer to the winter solstice, and 
from the winter round to the summer solstice, these 
intervals were found to be unequal.— This almost in- 
credible result was confirmed, by remarking that the 
shorter spaces from equinox to solstice, dividing the 
sun's annual route, into four equal portions, were 
passed over in unequal times. These results could 
not be doubted, for each observation, from year to 
year, confirmed them. They were received and re- 
corded, but the problem was handed down to succeed- 
ing generations for solution. 

In consequence of the oblique direction of the eclip- 
tic or sun's track, it was found difficult to retain its 
position in the mind. To assist in the recurrence to 
this important circle, a brazen circle was at length de- 
vised, and fastened permanently to another brazen 
circle, of equal size, under an angle, exactly equal to 
the inclination of the equator to the ecliptic. Circles, 
perpendicular to the equator, and passing through the 
solstices and equinoxes, completed the second astro- 
nomical instrument, the sphere. Having constructed 
this simple piece of machinery, it was mounted on an 
axis passing through its centre, and perpendicular to 
its equator, so as to revolve, as did the heavens, whose 
motions it was intended to represent. Having so 
placed the axis of rotation, that its prolongation would 
pass through the north star, this rude sphere came to 
play a most important part in the future investigations 
of the heavens. Its brazen equator and ecliptic were 



DISCOVERIES OF THE PRIMITIVE AGES. 59 

each divided into a certain number of equal parts, by 
reference to which the motion of the heavenly bodies 
might be followed, with far greater precision, than had 
ever been previously obtained. 

Armed with a new and more perfect instrument, the 
astronomer resumes his great investigation. Finding 
it now possible, to mark out the sun's path in the 
heavens, with certainty, by means of his brazen 
ecliptic, he discovers that the moon and planets in 
each revolution pass across the sun's track, and spend 
nearly an equal amount of time on the north and 
south sides of the ecliptic. This discovery led to a 
more accurate determination of the periods of revolu- 
tion of the planets. The interval was noted from one 
passage across the ecliptic to the next on the same 
side, and these intervals marked with accuracy the 
planetary periods. It now became possible to fix, with 
greater certainty, the relative positions of the sun and 
moon, and problems were once more resumed which 
had thus far baffled every effort of human genius. 
The phases of the moon, the very first point of inves- 
tigation, had never yet yielded up its hidden cause, 
and those terrific phenomena, solar and lunar eclipses, 
which had long covered the earth with terror and dis- 
may, were wrapped in mystery, and their explanation 
had resisted the sagacity of the most powerful and 
gifted intellects 

No one has ever witnessed the going out of the sun 
in dim eclipse, even now when its most minute phe- 
nomena are predicted with rigorous exactitude, with- 
out a feeling of involuntary dismay. What then must 
have been the effect upon the human mind in those 
ages of the world, when the cause was unknown, and 



60 STRUCTURE OF THE UNIVERSE. 

when these terrific exhibitions burst on earth's inhab- 
itants unheralded and unannounced ? Here then was 
an investigation, not prompted by curiosity alone, but 
involving the peace and security of man in all corning 
ages. We cannot doubt that the causes of the solar 
eclipse were first detected. It was observed, that no 
eclipse of the sun ever occurred, when the moon was 
visible. Even during a solar eclipse, when the sun's 
light had entirely faded away, and the stars and plan- 
ets stole gently upon the sight in the sombre and un- 
natural twilight, the moon was sought for in vain; she 
was never to be seen. This fact excited curiosity 
and gave rise to a careful and critical examination of 
the place in which the moon should be found, imme- 
diately after a solar eclipse ; and it was soon discovered 
that on the night following the day of eclipse, the 
moon was seen in her crescent shape very near to the 
sun and but a short distance from the sun's path. By 
remarking the moon's place, next before a solar eclipse 
and that immediately following, it was seen that at 
the time of the occurrence of the eclipse, the moon 
was actually passing from the west to the east side of 
the sun's place, and finally a little calculation showed 
that a coincidence of the sun and moon in the heav- 
ens took place at the precise time at which the sun 
had been eclipsed. The conclusion was irresistible, 
and the great fact was announced to the world, that 
the sun's light was hidden by the interposition of the dark 
body of the moon. 

Having reached this important result with en- 
tire certainty, the explanation of the moon's phases 
followed in rapid succession. For it now became 
manifest, that the moon shone with borrowed light. 



DISCOVERIES OF THE PRIMITIVE AGES. 61 

and that her brilliancy came from the reflected 
beams of the sun. This was readily demonstrated by 
the following facts. When the moon was so situated 
that the side next to the sun, (the illuminated one), 
was turned from the eye of the observer, (as was the 
case in a solar eclipse), then the moon's surface next 
to the observer, was always found to be entirety black. 
Pursuing her journey from this critical point, the moon 
was next seen near the sun, in the evening twilight, as 
a slender thread of light, a very small portion of her il- 
luminated surface being now visible. Day after day 
this visible portion increases, until finally the moon rises 
as the sun sets, full orbed and round,beingdirectly oppo- 
site the sun, and turning her entire illuminated surface 
towards the eye of the observer. By like degrees she 
loses her light as she approaches, and finally becomes 
invisible as she passes by the sun. From this exam- 
ination it became evident that the moon was a globu- 
lar body, non-luminous, and revolving in an orbit, com- 
prehended entirely within that described by the sun, 
and consequently, nearer to the earth than the sun. 
Having ascertained this fact, it was concluded that 
among all the moving heavenly bodies, the periods of 
revolution indicated their relative distances from the 
earth. Hence Mars was regarded as more distant 
than the sun, Jupiter more remote than Mars, and Sat- 
urn the most distant, as it was the slowest moving of 
all the planets. 

After reaching to a knowledge of the causes pro- 
ducing the eclipses of the sun and the phases of the 
moon, it remained yet to resolve the mystery of the 
lunar eclipse. It was far more difficult to render a 
satisfactory account of this phenomenon than either of 
F 



62 STRUCTURE OF THE UNIVERSE. 

the preceding. The light of the moon was not inter- 
cepted by the interposition of any opaque body, 
between it and the eye of the observer. No such 
body existed, and long and perplexing was the effort 
to explain this wonderful phenomenon. Finally it 
was observed that all opaque bodies cast shadows, 
in directions opposite to the source of light. Was it 
not possible that the light of the sun, falling upon the 
earth, might be intercepted by the earth, and thus 
produce a shadow which might even reach as far as 
the moon ? So soon as this conjecture was made, a 
series of examinations were commenced to confirm or 
destroy the theory. It was at once seen that in case 
the conjecture was true, no lunar eclipse could occur 
except when the sun, earth, and moon, were situated 
in the same straight line; a position which could never 
occur, except at the full or new of the moon. It was 
soon discovered that, it was only at the full, that lunar 
eclipses took place, thus confirming the truth of the 
theory, and fixing it beyond a doubt that the shadow 
of the earth falling on the moon, was the cause of her 
eclipse. The moon had already been shown to be 
non-luminous, and the moment the interposition of 
the earth, between it and its source of light, the sun, 
cut off its light, it ceased to be visible, and passed 
through an eclipse. The sphericity of the earth, 
which had been analogically inferred from that of the 
heavens, was now made absolutely certain — for it 
was remarked, that as the moon entered the earth's 
shadow, that the track of this dark shadow across the 
bright surface of the moon was always circular, which 
was quite impossible, for every position, except the 



DISCOVERIES OF THE PRIMITIVE AGES. 63 

earth, which cast this circular shadow, should be of 
a globular form. 

Having now attained to a clear and satisfactory 
explanation of the two grand phenomena, solar and 
lunar eclipses, the question naturally arose, why was 
not the sun eclipsed in each revolution of the moon ? 
and how happened it that the moon in the full, did 
not always pass through the earth's shadow? An 
examination of the moon's path among the fixed stars 
gave to these questions a clear and positive answer. 
It was found that the sun and moon did not perform 
their revolutions in the same plane. The moon's 
route among the stars crossed the sun's route under 
a certain angle, and it thus frequently happened, that 
at the new and full, the moon occupied some portion 
of her orbit too remote from that of the sun to render 
either a lunar or solar eclipse possible. 

Rapidly have we traced the career of discovery. 
The toil and watching of centuries have been con- 
densed into a few moments of time, and questions 
requiring ages for their solution have been asked, 
only to be answered. In connexion with the investi- 
gations just developed, and as a consequence of their 
successful prosecution, the query arose whether in 
case science had reached to a true exposition of the 
causes producing the eclipse of the sun, was it not 
possible to stretch forward in time, and anticipate 
and predict the coming of these dread phenomena? 

To those who have given but little attention to the 
subject, even in our own day, with all the aids of 
modern science, the prediction of an eclipse, seems 
sufficiently mysterious and unintelligible. How then 
it was possible, thousands of years ago, to accomplish 



64 STRUCTURE OF THE UNIVERSE. 

the same great object, without any just views of the 
structure of the system, seems utterly incredible. 
Follow me, then, while I attempt to reveal the train 
of reasoning which led to the prediction of the first 
eclipse of the sun, the most daring prophecy ever 
made by human genius. Follow in imagination, 
this bold interrogator of the skies to his solitary moun- 
tain summit — withdrawn from the world — surrounded 
by his mysterious circles, there to watch and ponder 
through the long nights of many — many years. But 
hope cheers him on, and smooths his rugged pathway. 
Dark and deep as is the problem, he sternly grap- 
ples with it, and resolves never to give over till 
victory crowns his efforts. 

He has already remarked, that the moon's track in 
the heavens crossed the sun's, and that this point of 
crossing was in some way intimately connected with 
the coming of the dread eclipse. He determines to 
watch and learn whether the point of crossing was 
fixed, or whether the moon in each successive revolu- 
tion, crossed the sun's path at a different point. If 
the sun in its annual revolution could leave behind 
him a track of fire marking his journey among the 
stars, it is found that this same track was followed 
from year to year, and from century to century with 
undeviating precision. But it was soon discovered, 
that it was far different with the moon. In case she 
too could leave behind her a silver thread of light 
sweeping round the heavens, in completing one revo- 
lution, this thread would not join, but would wind 
around among the stars in each revolution, crossing 
the sun's fiery track at a point west of the previous 
crossing. These points of crossing were called the 



DISCOVERIES OF THE PRIMITIVE AGES. 65 

moon's nodes. At each revolution the node occurred 
further west, until after a cycle of about nineteen 
years, it had circulated in the same direction entirely 
round the ecliptic. Long and patiently did the as- 
tronomer watch and wait, each eclipse is duly ob- 
served, and its attendant circumstances are recorded, 
when, at last, the darkness begins to give way and a 
ray of light breaks in upon his mind. He finds that 
no eclipse of the sun ever occurs unless the new moon 
is in the act of crossing the sun's track. Here was a 
grand discovery. — He holds the key which he believes 
will unlock the dread mystery, and now, with re- 
doubled energy, he resolves to thrust it into the wards 
and drive back the bolts. 

To predict an eclipse of the sun, he must sweep 
forward, from new moon to new moon, until he finds 
some new moon which should occur, while the moon 
was in the act of crossing from one side to the other 
of the sun's track. — This certainly was possible. 
He knew the exact period from new moon to new 
moon, and from one crossing of the ecliptic to another. 
With eager eye he seizes the moon's place in the 
heavens, and her age, and rapidly computes where 
she will be at her next change. He finds the new 
moon occurring far from the sun's track ; he runs round 
another revolution ; the place of the new moon falls 
closer to the sun's path, and the next yet closer, until 
reaching forward with piercing intellectual vigor, he 
at last, finds a new moon which occurs precisely at 
the computed time of her passage across the sun's 
track. Here he makes his stand, and on the day 
of the occurrence of that new moon, he announ- 
ces to the startled inhabitants of the world, that the 
f2 



66 STRUCTURE OF THE UNIVERSE. 

sun shall expire in dark eclipse — Bold prediction ! — 
Mysterious prophet ! with what scorn must the un- 
thinking world have received this solemn declaration. 
How slowly do the moons roll away, and with what 
intense anxiety does the stern philosopher await the 
coming of that day which should crown him with 
victory, or dash him to the ground in ruin and disgrace. 
Time to him moves on leaden wings ; day after day, 
and at last hour after hour, roll heavily away. The 
last night is gone — the moon has disappeared from 
his eagle gaze in her approach to the sun, and the 
dawn of the eventful day breaks in beauty on a slum- 
bering world. 

This daring man, stern in his faith, climbs alone to 
to his rocky home, and greets the sun as he rises and 
mounts the heavens, scattering brightness and glory 
in his path. Beneath him is spread out the popu- 
lous city, already teeming with life and activity. The 
busy morning hum rises on the still air and reaches 
the watching place of the solitary astronomer. The 
thousands below him, unconscious of his intense anx- 
iety, buoyant with life, joyously pursue their rounds 
of business, their cycles of amusement. The sun 
slowly climbs the heavens, round and bright and full 
orbed. The lone tenant of the mountain-top almost 
begins to waver in the sternness of his faith, as the 
morning hours roll away. But the time of his triumph, 
long delayed, at length begins to dawn ; a pale and 
sickly hue creeps over the face of nature. The sun 
has reached his highest point, but his splendor is dim- 
med, his light is feeble. At last it comes ! — Blackness 
is eating away his round disc, — onward with slow but 
steady pace, the dark veil moves, blacker than a thous- 



DISCOVERIES OF THE PRIMITIVE AGES. 67 

and nights, — the gloom deepens, — the ghastly hue of 
death covers the universe, — the last ray is gone, and 
horror reigns. A wail of terror fills the murky air, — 
the clangor of brazen trumpets resounds, — an agony 
of despair dashes the stricken millions to the ground, 
while that lone man, erect on his rocky summit, with 
arms outstretched to heaven, pours forth the grateful 
gushings of his heart to God, who had crowned his 
efforts with triumphant victory. Search the records 
of our race, and point me, if you can, to a scene more 
grand, more beautiful. It is to me the proudest vic- 
tory that genius ever won. It was the conquering of 
nature, of ignorance, of superstition, of terror, all at a 
single blow, and that blow struck by a single arm. — 
And now do you demand the name of this wonderful 
man ! Alas ! what a lesson of the instability of earthly 
fame are we taught in this simple recital. — He who 
had raised himself immeasurably above his race, — who 
must have been regarded by his fellows as little less 
than a god, who had inscribed his fame on the very 
heavens, and had written it in the sun, with a " pen 
of iron, and the point of a diamond," even this one 
has perished from the earth — name, age, country, are 
all swept into oblivion, but his proud achievement 
stands. The monument reared to his honor stands, 
and although the touch of time has effaced the letter- 
ing of his name, it is powerless, and cannot destroy 
the fruits of his victory. 

A thousand years roll by : the astronomer stands on 
the watch tower of old Babylon, and writes for pos- 
terity the records of an eclipse ; this record escapes 
destruction, and is safely wafted down the stream of 
time. A thousand years roll away : the old astrono- 



68 STRUCTURE OF THE UNIVERSE. 

mer 5 , surrounded by the fierce, but wondering Arab, 
again writes, and marks the day which witnesses the 
sun's decay. A thousand years roll heavily away : 
once more the astronomer writes from amidst the gay 
throng that crowds the brightest capital of Europe. 
Record is compared with record, date with date, rev- 
olution with revolution, the past and present are link- 
ed together, — another struggle commences, and another 
victory is won. Little did the Babylonian dream, that 
he was observing for one who after the lapse of 3000 
years, should rest upon this very record, the success- 
ful resolution of one of nature's darkest mysteries. 

We have now reached the boundary where the 
stream of discovery, which we have been tracing 
through the clouds and mists of antiquity, begins to 
emerge into the twilight of tradition, soon to flow on 
in the clear light of a history that shall never 
die. Henceforth our task will be more pleasing, be- 
cause more certain ; and we invite you to follow us 
as we attempt to exhibit the coming struggles and 
future triumphs of the student of the skies. 



LECTURE III. 

THEORIES FOR THE EXPLANATION OF THE MOTIONS OF 
THE HEAVENLY BODIES. 

If in tracing the career of astronomy in the primi- 
tive ages of the world, we have been left to pursue 
our way dimly, through cloud and darkness, — if re- 
grets rise up, that time has swept into oblivion the 
names and country of the early discoverers, in one re- 
flection there is some compensation — while the bright 
and enduring truths which they wrested from nature 
have descended to us, their errors, whatever they 
may have been, are forever buried with their names 
and their persons. We are almost led to believe that 
those errors were few and transient, and that the 
mind, as yet undazzled by its triumphs, questioned 
nature, with that humility and quiet perseverance, 
which could bring no response but truth. 

In pursuing the consequences flowing from the pre- 
diction of an eclipse, several remarkable results were 
reached, which we proceed to unfold. It will be re- 
collected, that to produce either solar or lunar eclip- 
ses, the new or full moon must be in the act of cross- 
ing the sun's annual track. This point of crossing, 
called the moon's node, became therefore an object of the 
deepest interest. Long and careful scrutiny revealed 
the fact of its movement around the ecliptic, in a period 

(69) 



70 STRUCTURE OF THE UNIVERSE. 

of eighteen years and eleven days, during which time 
there occur 223 new moons, or 223 full moons. If then, 
a new moon falls on the sun's track to produce a solar 
eclipse to-day, at the expiration of 223 lunations, 
again will the new moon fall on the ecliptic, and an 
eclipse will surely take place. Suppose then that all 
the eclipses, which occur within this remarkable pe- 
riod of 223 lunations, are carefully observed, and the 
days on which they fall recorded, on each and every 
one of these days, during the next period of 223 luna- 
tions, eclipses may be expected, and their coming fore- 
told. 

This wonderful period of eighteen years and eleven 
days, or 223 lunations, was known to the Chaldeans, 
and by its use eclipses were predicted, more than 3000 
years ago. It is likewise found among the Hindus, 
the Chinese, and the Egyptians, nations widely sepa- 
rated on the earth's surface, and suggesting the idea 
that it had its origin among a people even anterior 
to the Chaldeans. It is now known by the name of 
the Zaros. or Chaldean period. 

Let it not be supposed that the application of the 
Zaros to the prediction of eclipses, can in any way 
supersede modern methods. — While antiquity conten- 
ted itself with announcing the day on which the dark 
body of the moon should hide the sun, modern science 
points to the exact second on the dial, which shall 
mark the first delicate contact of the moon's dark 
edge with the brilliant disk of the sun. 

It would be a matter of great interest to fix the 
epoch of primitive discovery. Though this is impossi- 
ble, its high antiquity is attested by a few facts, to 
which we will briefly advert. We find among all the 



MOTIONS OF THE HEAVENLY BODIES. 71 

ancient nations, Chaldeans, Persians, Hindus, Chinese, 
and Egyptians, that the seven days of the week were in 
universal use, and what was far more remarkable, each 
of these nations named the days of the week after the 
seven planets, numbering the sun and moon among 
the planets. It is moreover found, that the order of 
naming is not that of the distance, velocity or brilliancy 
of the planets, and neither does the first day of the 
week coincide among the different nations ; but the 
order once commenced is invariably preserved by all. 
If we compute the probability of such a coincidence 
resulting, by accident, we shall find the chances mil- 
lions to one against it. We are therefore forced to 
the conclusion, that the planets were discovered, and 
the seven days of the week devised and named, by 
some primitive nation, from whom the tradition de- 
scended imperfectly, to succeeding generations. 

A remarkable discovery, made in the remote ages 
of the world, throws some farther light on the era of 
the primitive astronomical researches. — The release of 
the earth from the icy fetters of winter, the return of 
spring, and the revivification of nature, is a period 
hailed with uncommon delight, in all ages of the 
world. To be able to anticipate its coming, from 
some astronomical phenomenon, was an object of ear- 
nest investigation by the ancients. 

It was found that the sun's entrance into the equi- 
nox, reducing to equality the length of the day and 
night, always heralded the coming of the spring. 
Hence, to mark the equinoctial point among the fixed 
stars, and to note the place of some brilliant star 
whose appearance in the early morning dawn, would 
announce the sun's approach to the equator, was early 



72 STRUCTURE OF THE UNIVERSE. 

accomplished with all possible accuracy. This star 
once selected, it was believed that it would remain 
forever in its place. 

The sun's path among the fixed stars had been 
watched with success, and it seemed to remain abso- 
lutely unchanged, and hence the points in which it 
crossed the equator, for a long while were looked 
upon as fixed and immovable. And indeed centuries 
must pass away before any change could become sen- 
sible to the naked eye and its rude instrumental aux- 
iliaries. But a time arrives at last when the bright 
star which for more than five hundred years had, with 
its morning ray announced the season of flowers, is 
lost. It has failed to give its warning — spring has 
come, the forests bud, the flowers bloom, but the star 
which once gave promise, and whose ray had been 
hailed with so much delight by many generations, is 
no longer found. The hoary patriarch recalls the 
long experience of a hundred years, and now per- 
ceives, that each succeeding spring had followed more 
and more rapidly after the appearance of the sentinel 
star. Each year the interval from the first appear- 
ance of the star in the early dawn, up to the equality 
of day and night, had grown less and less, and now the 
equinox came, but the star remained invisible, and 
did not emerge from the suits beams until the equinox 
had passed. 

Long and deeply were these facts pondered and 
weighed. — At length truth dawned, and the discovery 
broke upon the unwilling mind, that the sun's path 
among the fixed stars was actually changing, and that his 
point of crossing the equator was slowly moving back- 
wards towards the west and leaving the stars behind. 



MOTIONS OF THE HEAVENLY BODIES. 73 

The same motion, only greatly more rapid, had been re- 
cognized in the shifting of the moon's node and in the 
rapid motion of the points at which her track crossed 
the equator. The retrograde motion of the equinoc- 
tial points, caused the sun to reach these points 
earlier than it would have done had they remained 
fixed, and hence arose the precession of the equinoxes. 

This discovery justly ranks among the most import- 
ant achieved by antiquity. Its explanation was in- 
finitely above the reach of human effort at that early 
day; but to have detected the fact, and to have mark- 
ed a motion so slow and shrouded, gives evidence of 
a closeness of observation worthy of the highest ad- 
miration. It will be seen hereafter, that the human 
mind has reached to a full knowledge of the causes 
producing the retrograde movement of the equinoxes 
among the stars. Its rate of motion has been deter- 
mined, and its vast period of nearly twenty-six thou- 
sand years has been fixed. Once revealed, the slow 
movement of the equinox, makes it a fitting hour 
hand, on the dial of the heavens, with which to meas- 
ure the revolutions of ages. As the sun's path has 
been divided into twelve constellations, each filling 
the twelfth part of the entire circuit of the heavens, for 
the equinox to pass the twelfth part of the dial, or 
from one constellation to the next, will require a pe- 
riod of more than two thousand years. Since the as- 
tronomer first noted the position of this hour hand on 
the dial of the stars, but one of its mighty hours of two 
thousand years, has rolled away. In case any record 
could be found, any chiselled block of granite, exhibit- 
ing the place of the equinox among the stars, at its 
date, no matter if ten thousand years had elapsed, 
G 



74 STRUCTURE OF THE UNIVERSE. 

we can reach back with certainty and fix the epoch 
of the record. 

No such monument has ever been found; but there 
are occasional notices of astronomical phenomena, 
found among the Greek and Roman poets, which at 
least give color to conjecture. Virgil informs us that 
" the White Bull opens with his golden horns the year." 

" Candidus auratis aperit cum cornibus annum, 
Taurus." 

This statement we know is not true, if applied to 
the age in which the poet wrote, and seems to be the 
quotation of an ancient tradition. If this conjecture 
be true, this tradition must have been carried down 
the stream of time for more than two thousand years, 
to reach the age in which the poet wrote. Although 
these conjectures are vague and uncertain, the fre- 
quent allusions to the constellations of the zodiac, in 
the old Hebrew Scriptures, and in the works of all 
ancient writers, sufficiently attest the extreme an- 
tiquity of these arbitrary groupings of the stars. 

In taking leave of the primitive ages of astronomy, 
and in entering on that portion of the career of 
research and discovery whose history has been pre- 
served, let us pause for a moment and consider the 
position occupied by the human mind at this remark- 
able epoch. 

Thus far the eye had done its work faithfully. 
Through long and patient watching, it had revealed 
the facts, from which reason had wrought out her 
great results. The stars grouped into constellations, 
glittered in the blue concave of a mighty sphere, 
whose centre was occupied by the earth. Within this 
hollow sphere, sun, moon and planets, kept their 



MOTIONS OF THE HEAVENLY BODIES. 75 

appointed courses, and performed their ceaseless jour- 
nies. Their wanderings had been traced, — their path- 
way in the heavens was known, — their periods de- 
termined, — the inclinations of their orbits fixed. So 
accurately had the eye followed the sun and moon, 
that it had learned to anticipate their relative posi- 
tions, their oppositions and conjunctions, till reaching 
forward, it had robbed the dread eclipse of its terrors, 
and had learned to hail its coming with delight. The 
pathway of the sun and moon among the stars had 
been scanned and studied, until their slowest changes 
had been marked and measured. 

Such were the rich fruits of diligence and persever- 
ance which descended from the remote nations of 
antiquity. With the advantage of these great dis- 
coveries, and the experience of preceding ages, it is 
natural to expect rapid progress, when science found 
its home among the bold, subtle, and inquisitive 
Greeks. He who entertains this expectation will 
meet with disappointment. Not that investigations 
were less constantly or perseveringly conducted, — not 
that less perfect means were employed, or less power- 
ful talent consecrated to the work; but because a point 
had been reached of exceeding difficulty. The era 
of discovery from mere inspection was rapidly draw- 
ing to a close. It was an easy matter to count the 
days from full moon to full moon, to watch a planet 
as it circled the heavens, from a fixed star until it re- 
turned to the same star again, to mark its stopping, 
its reversed motion, and its onward goings ; but it was 
a far different matter to rise to a knowledge of the 
causes of these stations and retrogradations, and to 
render a clear and satisfactory account of them. The 



70 STRUCTURE OF THE UNIVERSE. 

problem now presented, was to combine all the facts 
treasured by antiquity, all the movements exhibited 
in the heavens, and reduce them to simplicity and 
harmony. The Greek philosophers, from Plato down 
to the extinction of the last school of philosophy, 
recognized this to be the true problem, and essayed 
its solution, with an energy and pertinacity worthy 
of the highest admiration. 

Let us now examine the causes which arrested the 
progress ot astronomical discovery and held back the 
mind for a period of more than two thousand years. 
Surrounded as we are by the fall blaze of truth, ac- 
customed to the simplicity and beauty which now 
reign every where in the heavens, we find it next to 
impossible to realize the true position of those brave 
minds, which, enveloped in darkness, deceived by the 
senses, fettered by prejudice, struggled on and finally 
won the victory, whose fruits we enjoy. 

The most careful and philosophical examination of 
the heavens seemed to lead to the admitted truth, that 
the earth was the centre of all celestial motion. In 
the configuration of the bright stars there was no 
change. From age to age, from century to century, 
immovably fixed in their relative positions, they had 
performed their diurnal revolutions around the earth. 
They were ever of the same magnitude, of the same 
brilliancy. How impossible was this, on any hypothe- 
sis, except that of the fixed central position of the 
earth. Leaving the fixed stars, an examination of the 
motions of the sun and moon — their nearly uniform 
velocity — their invariable diameters in all portions of 
their orbits, demonstrated the central position of the 
earth with reference to them. To shake a faith thus 



MOTIONS OF THE HEAVENLY BODIES. 77 

firmly fixed, sustained by the evidence of the senses, 
consonant with every feeling of the mind, accordant 
with fact and reason, required a depth of research, 
and the development of new truths, only to be revealed 
after centuries of observation. 

Every effort, then, to explain the celestial phenom- 
ena, started with the undoubted fact, that the earth 
was the centre of all motion. Thus far, the mind had 
not reached the idea of apparent motion. If the moon 
moved, so equally did the sun. There was exactly 
the same amount of evidence to demonstrate the 
reality of the one motion, as the other ; neither were 
doubted. It would have been unphilosophical to reject 
the one, without rejecting the other. 

The centre of motion once determined, the nature 
of the curve described was so obviously presented to 
the eye, that it seemed impossible to hesitate for one 
moment. The circle was the only regular curve 
known to the ancients. Its simplicity, its beauty and 
perfection, would have induced its selection, even had 
there been a multitude of curves from which to choose. 
Its curvature was ever the same. It had neither be- 
ginning nor end. It was the symbol of eternity, and 
admirably shadowed forth the eternity of the motions 
to which it gave form. As if these considerations 
had required confirmation, every star and planet, the 
sun and moon, all described circles, in their diurnal 
revolution, and it seemed impossible to doubt that their 
orbitual motions were performed in the same beauti- 
ful curve. In truth, observation confirmed this con- 
jecture ; and the orbits of all the moving bodies, when 
projected on the concave heavens, were circles. That 
this curve, then, should have been adopted without 
g2 



78 STRUCTURE OF THE UNIVERSE. 

doubt or hesitation, is not to be wondered at. It came 
therefore, to be a fixed principle, that in all hypothe- 
ses devised to explain the phenomena of the heavens, 
circular motion and circular orbits, alone could be 
employed. 

To these great principles, of the central position of 
the earth, and the circular orbits, we must add that of 
the earth's immobility. This doctrine was undoubt- 
edly sustained by the evidence of all the senses which 
could give testimony. No one had seen it move, — 
had heard it move — had felt it move. How was it 
possible to doubt the evidence of the eye, the touch, 
the ear ? Here, then, was another incontrovertible 
fact, which even the most skeptical could not doubt, 
and which laid at the foundation of all effort to re- 
solve the problem under examination. 

With a full knowledge and appreciation of these 
facts, we are prepared to enter upon an examination 
of the career of astronomy, up to the- time when all 
darkness disappeared before the dawning of a day 
which should never end. The early Greek philoso- 
phers, little fitted by nature for close and laborious 
observation, rather chose to gather in travel the wis- 
dom which was garnered up in the temples, and 
among the priests of Egypt, and India. Returning to 
their native county, they theorised on the facts they 
had learned, and taught doctrines, which found their 
only support in trains of fanciful or specious reason- 
ing. Thus we find Pythagoras mingling the great 
discoveries of antiquity with theories the most vague 
and visionary. While gleams of truth flash occasion- 
ally through the darkness of his doctrines, they seem 
but fortunate guesses. His views were sustained by 



MOTIONS OF THE HEAVENLY BODIES. 79 

no solid argument, and rapidly sunk into forgetful- 
ness. This philosopher is said to have fixed the sun 
in the centre of his planetary system, and to have 
taught the revolution of the earth in an orbit; but to 
sustain this bold conjecture, the only reason assign- 
ed, was, that fire which composes the sun, was more 
dignified than earth, and hence should hold the more 
dignified position in the centre. We are not surprised 
that Hipparchus and Ptolemy, the true astronomers 
among the Greeks, should have rejected a doctrine 
sustained by so futile and absurd a reason. Mcetas, 
a follower of Pythagoras, is said to have gone farther 
than his master, and to have adopted the idea that 
the revolution of the heavens, was an appearance 
produced by an actual rotation of the earth on an axis, 
once in twenty-four hours. This extraordinary and 
almost prophetic announcement, unfortunately was 
not sustained by any solid argument. It was regarded 
as a vain dream, and soon was lost in oblivion. 

A crowd of theoretic philosophers filled for a long 
time the schools of Greece, contributing little to 
science, and diverting the mind from the only train 
of research which-could lead to any true results. At 
length a philosopher arose who restored investigation 
to its legitimate channel. Hipparchus, abandoning, 
for the present, all vain effort to explain the phe- 
nomena of the heavens, gave himself up to close, 
continuous, and accurate observation. He began with 
the movements of the sun in his annual orbit. By 
the construction of superior brazen circles, he meas- 
ured the daily motion of the sun during the entire 
year. He confirmed the discovery of the ancients, 
of the irregular or unequal progress of this luminary, 



80 STRUCTURE OF THE UNIVERSE. 

and fixed that point in the sun's orbit where it moved 
with greatest velocity. Year after year, did this devo- 
ted astronomer follow the sun, until finally he discov- 
ered that the point on the orbit, where its motion was 
swiftest, did not remain fixed, but was advancing in 
each revolution, at a very slow rate along the orbit. 
Having thus demonstrated and characterised the ir- 
regularity of the sun's motion, he directed his atten- 
tion to minute examinations of the moon, and reached 
results precisely similar. From these discoveries, it 
became manifest, that in case the motions of the sun 
and moon were circular and uniform, the earth did 
not occupy the exact centres of their orbits; for on 
this hypothesis any irregularity of motion would have 
been impossible. Here was a point gained. The 
exact central position of the earth was disproved in 
two instances, and even the amount of its eccentri- 
city, or distance from the true centre, determined. 
Retaining the circular and uniform motion of the 
sun and moon, the discovered irregularities were tol- 
erably well represented by the eccentric position 
of the earth, from whose surface these motions were 
measured. 

While pursuing these important researches, Hip- 
parchus resolved upon a work of extraordinary diffi- 
culty, which had never before been attempted, and 
which fully attests the grandeur and sagacity of his 
views. This enterprise was nothing less than num- 
bering the stars and fixing their positions in the heav- 
ens. This he actually accomplished, and his cata- 
logue of 1081 of the principal stars, is perhaps the 
richest treasure which the Greek school has transmit- 
ted to posterity. We cannot too much admire the 



MOTIONS OF THE HEAVENLY BODIES. 91 

disinterested devotion to science, which prompted this 
great undertaking, and the firmness of purpose which 
sustained the solitary observer, through long years of 
toil. It was a work for posterity, and could yield to 
its author no reward during his life. Conscious of 
this, his resolution never faltered, and grateful pos- 
terity crowns his memory with the^. well-earned title 
of Father of Astronomy. The noble example thus 
set by Hipparchus, was not lost on Ptoleirrv, justly the 
most distinguished among his immediate successors. 
An ardent student, a close observer, a patient and 
candid reasoner, Ptolemy collected and digested the 
discoveries and theories of his predecessors, and trans- 
mitted them, in connection with his own, successfully 
to posterity. Rejecting the absurd doctrine of the 
solid crystal spheres of Eudoxus, and the unsustained 
notions of Pythagoras, this bold Greek undertook the 
resolution of the great problem, which Plato had long 
before presented, and to accomplish which, so many 
unsuccessful efforts had been made. 

After a careful examination of all the facts and 
discoveries, which the world then possessed, adding 
his own extensive observations, Ptolemy promulged 
a system which bears his name, and which endured 
for more than fourteen hundred years. He fixed the 
earth as the great centre, about which the sun, the 
moon, the planets, and the starry heavens, revolved. 
Retaining the doctrine of uniform circular motion, he 
accounted for the irregularity in the movements of the 
sun and moon by the eccentric position of the earth 
in their orbits. — To explain the anomalous movement 
of the planets, he devised the system of cycles and 
epicycles. Every planet moved uniformly in the cir- 



82 STRUCTURE OF THE UNIVERSE. 

cumference of a small circle, whose centre moved 
uniformly in the circumference of a large circle, near 
whose centre the earth was located. By this ingenious 
theory, it was shown that a planet moving in the cir- 
cumference of its small circle might appear to retro- 
grade, to become stationary, and finally to advance 
among the fixed stars. Thus were all the phenomena 
known to the Greek astronomer, so satisfactorily ac- 
counted for, that it even became possible from this 
singular theory, to compute tables of the planetary 
motions, from which their places could be predicted 
with such precision, that the error, if any existed, es- 
caped detection by the rude instruments then in use. 

While the explanation of the celestial phenomena 
had constituted the principal object of the Greek as- 
tronomers, some rude efforts were commenced to de- 
termine the magnitude of the earth, and the relative 
distances of the sun and moon. The process adopted 
by Eratosthenes, two thousand years ago, to deter- 
mine the circumference of the earth, and its diameter, 
is essentially the same now employed by modern 
science. The results reached by the Greek astrono- 
mer, owing to an ignorance of the exact value of his 
unit, are lost to the world. 

When astronomy was banished from Greece, it 
found a home among the Arabs. When darkness and 
gloom wrapped the earth through ten long centuries, 
and human knowledge languished, and art died, and 
genius slumbered, it is a remarkable fact, that astron- 
omy during that long period of ignorance, instead of 
being lost, was actually slowly advancing, and when 
the dawn of learning once more broke on Europe, the 
astronomy of the Greeks, improved by the Arabs and 



MOTIONS OF THE HEAVENLY BODIES. 83 

the Persians, was preserved in the great work of 
Ptolemy, and transmitted to posterity. 

It is true that no change had been wrought in the 
Greek theory, but observations had been multiplied 
and slow changes measured, which prepared the way 
for the discoveries which were soon to succeed. On 
the revival of learning in Europe, the literature and 
science of the Greeks and Romans rapidly spread, and 
gained an astonishing ascendancy over the human 
mind. Indeed, theirs was the only science, the only 
wisdom. Time honored, and venerable with age, the 
philosophy of Aristotle, the geometry of Euclid, and 
the astronomy of Ptolemy, filled the colleges and uni- 
versities, and fastened itself upon the age, with a te- 
nacity, which permitted no one to question or doubt, 
and which seemed to defy all further progress. — Such 
was the state of science and the world, when Coper- 
nicus consecrated his genius to the examination of the 
heavens. 

To a mind singularly bold and penetrating, Coper- 
nicus united habits of profound study and severe ob- 
servation. Deeply read in the received doctrines of 
science, he examined with the keenest interest, every 
hint which the philosophers of antiquity had left on 
record concerning the system of nature. For more 
than thirty years he watched, with unceasing per- 
severance, the movements of the heavenly bodies. 
By the construction of superior instruments, he com- 
pared the observed places of the sun, moon and plan- 
ets, with their positions computed from the best ta- 
bles founded on the theory of Ptolemy. The hy- 
pothesis of uniform circular motion, had originally 
been adopted, to preserve the simplicity of nature, 



84 STRUCTURE OF THE UNIVERSE. 

and with true philosophy. But as one irregularity- 
after another had been discovered in the movements 
of the heavenly bodies, each of which must be ex- 
plained on the circular hypothesis, one circle had 
been successively added to another, eccentrics and 
epicycles, equants and difFerents, until to preserve 
simplicity, the system had grown to the most ex- 
travagant complexity. The primitive idea of sim- 
plicity was a just one, founded in nature, and adopt- 
ed in reason. But after thirty years of vain effort to 
harmonize the phenomena of the heavens with the 
theory of Ptolemy, after entangling himself in a maze 
of complexity in his effort to preserve simplicity, Co- 
pernicus was at last driven to doubt, and doubt soon 
grew into disbelief. By a close examination of the mo- 
tions of Mercury and Venus, he found that these planets 
always accompanied the sun, participated in its move- 
ments, and never receded from it except to limited 
distances. The uniformity of their oscillations, from 
the one side to the other of the sun, suggested their 
revolution about that luminary, in orbits, whose planes 
passed nearly through the eye of the observer. The 
Egyptians had reached to this doctrine, had commu- 
nicated it to Pythagoras, who taught it to his country- 
men, nearly two thousand years before the time of 
Copernicus. 

If then simplicity imperiously demanded the aban- 
donment of the earth as the great centre of motion, 
in the search for a new centre, a multitude of circum- 
stances pointed to the sun. It was the largest and 
most brilliant of all the heavenly bodies. It gave 
light to the moon and planets. It gave life to the 
earth and its inhabitants. It was certainly accom- 



MOTIONS OF THE HEAVENLY BODIES. 85 

panied by two satellites, and above all, it was so 
related to the earth, that if motion in the one was 
abandoned, it must instantly and without a moment's 
hesitation, be transferred to the other. Long did the 
philosopher hesitate, perplexed with doubts, surroun- 
ded by prejudice, embarrassed with difficulties, but 
finally rising superior to every consideration save 
truth, he quitted the earth, swept boldly through 
space, and planted himself upon the sun. With an 
imagination endowed with the most extraordinary 
tenacity, he carried with him all the phenomena of 
the heavens, which were so familiar to his eye, while 
viewed from the earth. A long train of investigation 
was now before him. He commences with his now 
distant earth. Its immobility is gone — he beholds it 
sweeping round the heavens in the precise track once 
followed by the sun. The same constellations mark 
its career, the same periodic time, the same inequali- 
ties of motion; all that the sun has lost the earth has 
gained. 

Thus far the change had been without results. He 
now gives his attention to the planets. Here a most 
beautiful scene broke upon his senses. The complex 
wanderings of the planets, their stations, their retro- 
grade motions, all disappeared, and he beheld them 
sweeping harmoniously around him. The earth, de- 
prived of her immobility, started in her orbit, joined 
her sister planets, and gave perfection to the system. 
The oscillations of Mercury and Venus were convert- 
ed into regular revolutions, still holding their places 
nearest to the sun ; then came the earth, next Mars, 
and Jupiter, and last of all Saturn away in the dis- 
tance, slowly pursuing his mighty orbit. All were 
H 



86 STRUCTURE OF THE UNIVERSE. 

moving in the same direction, their paths filling the 
same belt of the heavens. 

Charmed with this beautiful scene, the philosopher 
turns to an examination of the moon. Was she, too, 
destined to take her place among the planets. A short 
investigation revealed her true character. She could 
not be a planet revolving about the sun interior to the 
earth's orbit, for if so she would have imitated the os- 
cillations of Mercury and Yenus. — She was not a 
planet revolving around the sun, exterior to the orbit 
of the earth, for in that case she must have imitated 
the stations and retrogradations of Mars, Jupiter, and 
Saturn. The invariability of her diameter as seen 
from the earth, joined to these considerations, estab- 
lished the fact of her secondary character, and like a 
favorite minister who accompanies his dethroned mon- 
arch in his exile, so did the faithful moon cling to the 
earth and follow it in its wanderings through space. 

Such is the beautiful system wrought out by the 
great Polish philosopher. Far from perfect, it was 
founded in truth, and although improvement might and 
must come, revolution could never shake its firm foun- 
dation. — While the more prominent irregularities in 
the planetary motions were removed by constituting 
the sun the centre of motion, there yet remained an 
increase and decrease in the orbitual velocities of all 
the planets, now including the earth among the num- 
ber, which were inexplicable. The planets did not 
revolve, then, in circles whose exact centre was occu- 
pied by the sun. The moon's orbit was not a cir- 
cle, whose exact centre was the earth ; and to ex- 
plain these unfortunate irregularities, Copernicus, 
clinging to circular motion, as the world had done for 



MOTIONS OF THE HEAVENLY BODIES. 87 

2000 years, was driven to adopt the same expedients 
which characterized the theories of Ptolemy : the ec- 
centric and epicycle were fastened upon the new sys- 
tem of astronomy. Yet another difficulty embarrassed 
the mind of Copernicus. In giving to the earth a ro- 
tation on its axis once in twenty-four hours, he ex- 
plained the apparent revolution of the starry heavens. 
This axis of rotation, it was readily seen, must ever re- 
main parallel to itself in the annual revolution of the 
earth in its orbit. Being in this way carried round 
such a vast circumference, the prolongation of the axis 
ought to pierce the northern heavens in a series of 
points which would form a curve so large as not to 
escape detection. But no such curve appeared, the 
north pole of the heavens, scrutinized with the most 
delicate instruments, preserved its position, immovably 
throughout the entire revolution of the earth in its 
orbit, and to escape from this difficulty there was no 
alternative but to admit that the distance of the 
sphere of the fixed stars was so great that the diameter 
of the earth's orbit, equal to 200,000,000 of miles, 
was absolutely nothing, when compared with that 
mighty distance. 

Under these circumstances, it is not wonderful that 
Copernicus should have promulged his system with 
extreme diffidence and only after long delay ; indeed 
his great work, setting forth his doctrines, was never 
read by its author in print, and only reached him in 
time to cheer his dying moments. 

We cannot then be surprised, that the new system 
was received with doubt and distrust, or rather that it 
was for a long while absolutely rejected. — The pro- 
gress of truth is ever slow, while error moves with 



88 STRUCTURE OF THE UNIVERSE. 

rapid pace. The reason is obvious. — Error is seized 
by a class of minds, which asks no evidence ; while 
the searchers for truth, adopt it only after the most 
deliberate examination. 

But the revolution had been commenced. A few 
bold minds were struck with the simplicity and 
beauty of the conjectures of Copernicus ; and when the 
exigencies of the age demand genius, it seems to rise 
spontaneously. The mind had persevered in a sys- 
tem founded in reason, and which nothing short of this 
very perseverance could have demonstrated to be er- 
roneous. Like the traveler, who is uncertain which 
of two roads to take, he reflects, reasons, and decides, 
and even if his choice be a wrong one, it would be folly 
to stop before fully convinced that he had chosen 
erroneously. 

But the mind is once again in the path of truth; and 
after wandering twenty long centuries in darkness, 
which grew deeper and deeper, the change from dark- 
ness to light gives vigor to its movements, and its 
future achievements are destined to be rapid and 
glorious. 

Here let us pause for a moment, on the boundary 
which divides ancient from modern science, and 
glance at the collateral circumstances which were 
found to modify and retard the investigations which 
had commenced. The old doctrines of philosophy and 
astronomy, had become intimately interwoven with 
human society. Ptolemy, and Plato, and Aristotle, were 
regarded with a sort of reverential awe. Even the 
church, not following, but leading the world in this 
profound respect for ancient philosophy, pronounced 
the doctrines of Ptolemy in accordance with the reve- 



MOTIONS OF THE HEAVENLY BODIES. 89 

lations of scripture, and girdled them with the fires of 
persecution, through which alone their sacredness 
could be attacked. Thus entrenched and defended by 
prejudice, by society and by religion, none but the most 
daring spirit would enter the conflict against such un- 
equal odds. Conscious of these difficulties, Coperni- 
cus had wisely avoided collision, and gave his doc- 
trines to the world with such caution as not to pro- 
voke attack. But this armed neutrality could not 
long endure. If the new doctrine were founded in 
error, left to itself it would never advance, and would 
soon quietly sink into oblivion. On the contrary, should 
it prove to be based upon truth, no power could arrest 
its progress, or stay its development. The contest 
must come sooner or later, and demanded in those 
who should battle for the truth the rarest qualities. 

Copernicus had merely commenced the examination 
of his bold conjecture, A life time was too short to 
accomplish more. He had transferred the centre of 
motion from the earth to the sun, and rested the truth 
of his hypothesis on a diminished complexity in the 
celestial phenomena. In case the true centre had 
been found, it now remained to determine^ the exact 
curves in which the planets revolved, the laws regu- 
lating their motion, and the nature of the bond which, 
it was now suspected, united the planetary worlds 
into one great system. The resolution of these pro- 
found questions was reserved for Kepler, who has 
without flattery been termed the legislator of the 
heavens, and who has earned the reputation of being 
first in fact and first in genius among modern astrono- 
mers. He united in the most perfect manner, all the 
qualifications of a great discoverer. Ardent, enthusi- 
h2 



90 STRUCTURE OF THE UNIVERSE. 

astic, and subtle, he pursued his investigations with 
a keen and restless activity. Patient, laborious, and 
determined, difficulties shrunk at his approach and 
obstacles melted before him. Unprejudiced and pious, 
he sought for truth in the name and invoking ever 
the guidance of the great Author of truth. If his 
theories were not actually deduced from facts, when 
formed, no test was too severe, and nothing short of 
a rigid coincidence with fact could satisfy the exact- 
ing mind of this wonderful genius. Realizing fully 
the difficulty and importance of the researches before 
him, once commenced, his perseverance knew no 
limit, and the fertility of his imagination was utterly 
inexhaustible. 

Such was the man to whom the interests of science 
at this critical juncture were committed. Having 
adopted as an hypothesis, the central position of the 
sun, and the revolution of the earth and planets 
around this centre, he determined to discover the true 
nature of the planetary orbits, and find if possible, 
some single curve which would explain the orbitual 
motions of the celestial bodies. To accomplish this 
difficult enterprise, Kepler wisely determined to con- 
line his efforts and investigations to one single planet, 
and Mars was selected as the subject for experiment. 
He commenced by a rigorous comparison between the 
observed places of the planet and those given by the 
best tables which could be computed by the circular 
theory. Sometimes the predicated and observed places 
agreed well with each other, and hope whispered that 
the true theory had been found; but pursuing the 
planet onward in its sweep around the sun, it would 
begin to diverge from its theoretic track, its distance 



MOTIONS OF THE HEAVENLY BODIES. 91 

would increase until it became evident that the theory 
was false, and must be abandoned. 

Nothing daunted, the ardent philosopher consoled 
himself with the thought, that among all possible 
theories which the mind could frame, one had been 
stricken from the list, and a diminished number re- 
mained for examination. This was a new mode of 
research, and in case the number of theories was not 
too great, and the patience of the philosopher suffi- 
ciently enduring, a time would come, sooner or later, 
when success must reward his labors. Thus did 
Kepler toil on subjecting one hypothesis after another 
to the ordeal of rigid experiment, until no less than 
nineteen had been tested with the utmost severity, 
and all were rejected. Eight years of incessant labor 
had been devoted to this examination. He had ex- 
hausted every combination of circular motion which 
the fertility of his imagination could suggest. They 
had all utterly failed. — The charm was ended, and he 
finally broke away from the fascination of this beau- 
tiful curve, which for five thousand years had so be- 
wildered the human mind, and boldly pronounced it 
impossible to explain the planetary motions with any 
circular hypothesis. This at least was a great nega- 
tive triumph. If he had not found the curve in which 
the planets revolved, he had found what it could not 
be, and released from all future embarrassment from 
eccentrics and epicycles, he now pursued a lofty and 
independent train of investigation. 

Leaving forever the circle, the next simplest curve 
is called the ellipse, an oval figure, which when but 
little flattened very nearly resembles the circle in form, 
but enjoys very different properties. All diameters of 



92 STRUCTURE OF THE UNIVERSE. 

a circle are equal. The diameters of an ellipse are 
unequal. The centre of the circle is equally distant 
from all points on the circumference. No such point 
exists in the ellipse ; but two curious points are found 
on its longest diameter, possessing the remarkable 
property of having the sum of the lines joining them 
with any point of the curve constantly equal to the 
longest diameter. Each of these points is called a 
focus. This beautiful curve, with its singular proper- 
ties, had been discovered by the Greek mathemati- 
cians ; but not remarking its use in nature, it had 
hitherto been regarded only as an object of amusing 
speculation. To this curve did Kepler apply, when 
driven from the circular hypothesis, and again com- 
menced his system of forming hypotheses, and hunting 
them down, as he termed his scrutinizing process. As 
in the circular hypothesis the sun had at first been lo- 
cated in the centre, so in commencing the elliptic theory 
the centre of the longest diameter was made the cen- 
tre of motion. Buoyant with hope, the astronomer 
sets out to follow the planet around its elliptic orbit ; 
but although for a short distance its movements were 
well represented, it finally broke away from the elliptic 
track, and bid defiance to the central hypothesis. But 
Kepler was not in the least disheartened with this 
first effort — He now shifts the sun to the focus of the 
ellipse, constructs his orbit, starts once more on the 
track of the planet, watches it as it sweeps onward 
around the sun, the elliptic orbit holds it as it moves, 
farther and still farther. — Half its revolution is per- 
formed and there is no diverging, onward it flies, — the 
goal is won. — Triumph crowns the philosopher, the 
orbit is found ! 



MOTIONS OF THE HEAVENLY BODIES. 93 

Thus was accomplished one of the most important 
discoveries which the mind had ever reached. The 
elliptic orbit of Mars, rapidly led to those of the other 
planets, and to that of the moon, and Kepler pro- 
claimed to the world his first great law, in the follow- 
ing language : Planets revolve in elliptic orbits about the 
sun, which occupies the common focus of all these orbits. 

This law swept forever from the heavens and from 
astronomy those complications which had stood the 
test of centuries, nay of thousands of years. Their 
mysterious power was paralyzed by this single touch 
of the enchanter's wand, and they fled from the skies. 
The circle was as simple and beautiful as ever, but its 
divine character was gone, and the gods or angels 
who had so long held their abodes in the planets, were 
exiled from their homes. — The dawn of modern science 
broke in beauty on the world. 

Kepler having been so signally rewarded by this 
great discovery, now turned his attention to an inves- 
tigation of the first importance, one indeed which was 
indispensably necessary to render his first discovery 
available. As the planets were now known to re- 
volve in ellipses, and as their motion was found by 
observation to be unequal in different parts of their 
orbits, it became a matter of the first consequence to 
ascertain some simple law, regulating the orbitual 
motion, and by means of which a planet might be 
readily followed, and its places computed. To detect 
this law, in whose existence Kepler seems to have 
entertained the most unwavering faith, a figure 
was drawn representing the orbit of Mars, the sun 
occupying one of the foci of the curve. — On the cir- 
cumference of this curve the places of the planets were 



94 STRUCTURE OF THE UNIVERSE. 

marked down as observation had determined them ; 
and here commenced a series of examinations which 
finally led to the knowledge of the second great law 
of the planetary motions, which may be thus an- 
nounced. If a line be drawn from the centre of the sun, to 
any planet, this line as it is carried forward by the planet, 
will sweep over equal areas in equal portions of time. — 
This law accorded in the most perfect manner with 
fact, and gave at once the power of following, and 
from the mean motion, computing the place of any 
planet ; a triumph which all the complexity of older 
systems had failed ever to accomplish. 

Any other mind less adventurous than that of Kep- 
ler, might have been satisfied with these two great dis- 
coveries. The precise curves described by the planets 
and a law regulating their motions in their orbits, 
sufficed to render all the phenomena of the heavenly 
bodies not only explicable, but susceptible of accurate 
prediction. — There seemed nothing more to be added. 
— Kepler did not think so. He conceived the idea 
that the solar system was not a mere assemblage of iso- 
lated planets revolving about a common centre, but a 
great associated system, in which some common bond 
of union existed, which once found, would present the 
solar system in a new and true light. 

This bond he believed existed in some hidden rela- 
tion between the times occupied by the planets in de- 
scribing their orbits, and their distances from the sun. 
In the history of this remarkable research, we are pre- 
sented with one of the brightest examples of the 
fruits of perseverance. If some superior power, some 
spirit from a brighter world, had revealed to the mind 
of Kepler, the actual existence of some relation be- 



MOTIONS OF THIL HEAVENLY BODIES. 95 

tween the planet's periods and distances, and had 
proposed to him to discover this hidden law, there 
would have been a definite object before the astrono- 
mer, and to have persevered in the pursuit of this 
object, would have been within the limits of proba- 
bility, even if a lifetime were exhausted in fruitless 
efforts. But to excite in his own mind a faith suffi- 
ciently strong in the existence of a law of which there 
existed not the slightest evidence, and to have perse- 
vered in its research for seventeen long years of labo- 
rious effort, seems almost incredible. 

There is an immense difference between the pursuit 
which resulted in the discovery of the first two laws 
of Kepler, and the third one. In seeking for the curve 
described by the planets, it was looking for that, which 
must have an existence; and in tracing the law of a 
planet's motion, it was absolutely impossible to follow 
a planet, or predict its positions, without such a law 
But in seeking for a bond of union among the planet- 
ary periods and distances, it was a search for that, 
which it was believed had no existence, except in the 
wild imagination of this extraordinary philosopher. 
The history of mind scarcely furnishes an example in 
any degree parallel, if we except perhaps the heroic 
fortitude which marked the career of Columbus. — Yet 
even the great Genoese was in possession of solid 
facts on which to base his reasoning. He saw evi- 
dences of the existence of another hemisphere, which 
the superficial could never realize. Kepler, more bold, 
more grand, more sublime, dreamed of nothing less than 
a brotherhood of worlds, a mighty and magnificent 
scheme of vast revolving orbs. Should success crown 
his efforts, the most brilliant results would follow. 



96 STRUCTURE OF THE UNIVERSE. 

The distance of a single planet from the sun once ob- 
tained, and the periodic time of all being known, the 
distances might then be found for each individual in 
the entire system, without even directing an instru- 
ment to the heavens. Here then was a prize to 
reach which no time, or pains, or labor could be mis- 
applied. Its return would be a hundred fold. 

But where was the prize to be sought? Even ad- 
mitting that some common bond did bind the circling 
worlds into one harmonious system, did it exist in 
some hidden relation between their periods of revolu- 
tions, their distances, their magnitudes, their densi- 
ties ? or was it to be sought in some analogy between 
the distances and periodic times? After long and de- 
liberately pondering this great problem, Kepler de- 
cided that the strongest probability suggested that 
the distances of the planets, and their periods of rev- 
olution, would in some way contain the mysterious 
bond of union. Here then did this daring mind con- 
centrate its energies ; and his purpose once fixed, he 
marches steadily forward in his research with a cour- 
age which no defeat conld daunt, and a perseverance 
which knew no limit but success. 

Before announcing the final result, let me explain 
two terms employed in its statement. The square of 
any quantity results by multiplying it by itself. The 
cube comes from multiplying the square by the number. 
The square of a planet's period, or the cube of its dis- 
tance, are known the moment we know the period, 
and distance, by applying the simple rules of arith- 
metic. After Kepler had exhausted all simple rela- 
tions between the periods and distances of the planets, 
in no degree shaken in his lofty faith, he proceeded to 



MOTIONS OF THE HEAVENLY BODIES. 97 

try all possible relations between the squares of the 
periods and distances ; but with as little success. 
Nothing daunted, he proceeded to investigate the pos- 
sible relations between the cubes of the periods and 
distances. Here again he was foiled ; no law exhibited 
itself. — He returned ever fresh to the attack, and now 
commenced a series of trials involving the relations 
between the simple periods and the squares of the 
distances. Here a ray of hope broke in upon his 
dim and darkened path. 

No actual relation existed, yet there was a very 
distant approximation, enough to excite hope. — He 
then tried simple multiples of the periods and the 
squares of the distances — all in vain. He finally 
abandoned the simple periods and distances, and rose 
to an examination of the relations between the squares 
of these same quantities. — Gaining nothing here, he 
rose still higher, to the cubes of the periods and dis- 
tances ; — no success, until finally he tried the propor- 
tion existing between the squares of the periods in 
which the planets perform their revolutions and the 
cubes of their distances from the sun. — Here was the 
grand secret, but, alas ! in making his numerical com- 
putations, an error in the work vitiated the results, 
and with the greatest discovery which the mind ever 
achieved in his very grasp, the heart-sick and toil- 
worn philosopher turned away almost in despair from 
his endless research. 

Months rolled round, and yet his mind with a sort of 
keen instinct, would recur again and again to this last 
hypothesis . Guided by some kind angel or spirit whose 
sympathy had been touched by the unwearied zeal of 
the mortal,, he returned to his former computations, 
I 



98 STRUCTURE OF THE UNIVERSE. 

and with a heaving breast, and throbbing heart, he 
detects the numerical error in his work, and com- 
mences anew. The square of Jupiter's period is to 
the square of Saturn's period as the cube of Jupiter's 
distance is to some fourth term, which Kepler hoped 
and prayed might prove to be the cube of Saturn's 
distance. With trembling hand, he sweeps through 
the maze of figures ; the fourth term is obtained ; 
he compares it with the cube of Saturn's distance. — 
They are the same ! — He could scarcely believe his 
own senses. He feared some demon mocked him. — 
He ran over the work again and again — He tried the 
proportion, the square of Jupiter's period to the square 
of Mars' period as the cube of Jupiter's distance to a 
fourth term, which he found to be the cube of the dis- 
tance of Mars. — Till finally full conviction burst upon 
his mind : he had won the goal, the struggle of seven- 
teen long years was ended, God was vindicated, and 
the philosopher in the wild excitement of his glorious 
triumph, exclaims : 

" Nothing holds me. I will indulge my sacred fury ! 
If you forgive me I rejoice; if you are angry I can 
bear it. The die is cast. The book is written, to be 
read either now, or by posterity, I care not which. 
— It may well wait a century for a reader, since God 
has waited six thousand years for an observer ! " 

More than two hundred years have rolled away 
since Kepler announced his great discoveries . Science 
has marched forward with swift and resistless energy. 
The secrets of the universe have been yielded up under 
the inquisitorial investigations of god-like intellect. 
The domain of the mind has been extended wider and 
wider. One planet after another has been added to 



MOTIONS OF THE HEAVENLY BODIES. 99 

our system ; even the profound abyss which separates 
us from the fixed stars has been passed, and thou- 
sands of rolling suns have been descried, swiftly flying 
or majestically sweeping through the thronged regions 
of space. But the laws of Kepler bind them all, — 
satellite and primary — planet and sun — sun and sys- 
tem — all with one accord, proclaim in silent majesty, 
the triumph of the hero philosopher. 



LECTURE IV. 

DISCOVERY OF THE GREAT LAWS OF MOTION AND 
GRAVITATION. 

The remarkable discoveries which had rewarded 
the researches of Kepler, confirmed in the most per- 
fect manner the doctrines of Copernicus, flowing as 
they did from his prominent hypothesis, the central 
position of the sun. Having reached to the true laws 
of the planetary motions, the whole current of astro- 
nomical research was changed. New methods were 
demanded, and more delicate means of observation 
must be brought into use before the data could be 
furnished for new discoveries. Henceforward as- 
tronomy could only advance by the aid of kindred 
sciences. Mathematics, optics, and above all, me- 
chanical philosophy, were to become the instruments 
of future conquests. 

The philosophy of Aristotle, though very far from 
deserving it, wielded quite as extensive an influence 
over the age, as did the astronomy of Ptolemy. It 
appears, indeed, that the followers of Aristotle re- 
garded their master as absolutely infallible, and gave 
to his doctrines a credence so firm, that even the 
clearest experiments, the most undeniable evidence 
of the senses were sooner to be doubted than the doc- 
trines of the divine Greek. To attack and destroy a 

1 2 MOD 



102 STRUCTURE OF THE UNIVERSE. 

system so deeply rooted in the prejudices of the age, 
required a mind of extraordinary courage and power, 
a mind deeply imbued with the love of truth, quick in 
its perceptions, logical in argument, and firm in the 
hour of trial. 

Such a mind was that of the great Florentine phi- 
losopher, Galileo Galilei, the senior, friend, and con- 
temporary of Kepler. Indeed the exigencies of the 
age seem to have given birth to three men, whose 
peculiar constitutions fitted them for separate spheres, 
each of the highest order, each in some measure in- 
dependent, and yet all combining in the accomplish- 
ment of the great scientific revolution. While Tycho, 
the noble Dane, immured within the narrow limits of 
his little island, watching from his sentinel towers 
the motions of the stars, noting with patient and 
laborious continuity, the revolutions of the sun, moon 
and planets, was accumulating the materials which 
were to furnish the keen and inquisitive mind of 
Kepler with the means of achieving his great tri- 
umphs — Galileo, with a giant hand, was shaking to 
their foundations the philosophical theories of Aris- 
totle, and startling the world with his grand mechani- 
cal discoveries. But for the observations of Tycho, 
Kepler's laws could not have been revealed; — but for 
the magic tube of Galileo, these laws had been the 
ne plus of astronomical science. Thus do we witness 
the rare spectacle of three exalted intellects, contem 
poraneously putting forth their diverse talents in the 
accomplishment of one grand object. The Dane, the 
German, and the Italian, divided by language and by 
country, united in the pursuit of science and of truth. 

Called to Pisa to discharge the duties of a philo- 



LAWS OF MOTION AND GRAVITATION. 103 

sophical teacher, Galileo was not long in detecting 
the extravagant philosophical errors of Aristotle, 
which had been implicitly received for more than 
twenty centuries. He continued to teach the text of 
his old master, but it was only to expose its unsound 
and false philosophy to his wondering and incredu- 
lous pupils. A desecration so monstrous, could not 
long escape exposure and punishment. Indeed the 
Florentine made no secret of his teachings. The 
Aristotelians made common cause against the young 
philosophical heretic, and he was warned to desist 
from his heresy. Galileo gave for answer to his 
opponents, that he was ready to relinquish his new 
views the moment they were shown by experiment to 
be false ; on the other hand, he demanded of them 
equal candor, and proposed to refer the matter in con- 
troversy to the tribunal of experiment. 

Aristotle, in discussing the laws of falling bodies, 
affirmed the principle, that the velocity acquired by 
any falling body, was in the direct proportion of its 
weight; and if two bodies of unequal weight com- 
menced their descent from the same height, at the 
same moment, the heavier would move as many times 
swifter than the lighter, as its weight exceeded 
that of the smaller body. Galileo doubted the truth 
of this principle, and on subjecting it to the test of 
experiment, he saw instantly that its variation from 
fact was wide as it could be. The obvious character 
of this experiment, its freedom from all chances of 
deception, and the importance of the principle in- 
volved, induced the young philosopher to select it as 
the test, and to challenge his opponents to a public 
demonstration of the truth or falsehood of their ok] 



104 STRUCTURE OF THE UNIVERSE. 

system of philosophy. — The challenge was accepted. 
The leaning tower of Pisa presented the most conveni- 
ent position for the performance of these experiments, 
on which Galileo so confidently relied for triumphant 
demonstration of the error of Aristotle ; and thither on 
the appointed day the disputants repaired, each party 
perhaps with equal confidence. It was a great crisis 
in the history of human knowledge. On the one side, 
stood the assembled wisdom of the universities, re- 
vered for age and for science, venerable, dignified, 
united and commanding. Around them thronged the 
multitude, and about them clustered, the associations 
of centuries. On the other, there stood an obscure 
young man, with no retinue of followers, without 
reputation or influence, or station. But his courage 
was equal to the occasion ; confident in the power of 
truth, his form is erect, and his eye sparkles with 
excitement. 

But the hour of trial arrives. The balls to be em- 
ployed in the experiments are carefully weighed and 
scrutinized to detect deception. The parties are satis- 
fied. The one ball is exactly twice the weight of the 
other. The followers of Aristotle maintain that when 
the balls are dropped from the top of the tower, the 
heavy one will reach the ground in exactly half the 
time employed by the lighter ball. Galileo asserts that 
the weights of the balls do not affect their velocities, 
and that the times of descent will be equal ; and here 
the disputants join issue. — The balls are conveyed to 
the summit of the lofty tower. The crowd assembles 
round the base — the signal is given — the balls are 
dropped at the same instant, and swift descending, at 
the same moment they strike the earth. Again and 



LAWS OF MOTION AND GRAVITATION. 105 

again is the experiment repeated, with uniform re- 
sults. Galileo's triumph was complete. Not a shadow 
of doubt remained ; but far- from receiving, as he 
had hoped, the warm congratulations of honest con- 
viction — private interest, the loss of place, and the 
mortification of confessing false teaching, proved too 
strong for the candor of his adversaries. — They clung 
to their former opinions with the tenacity of despair, 
and assailed the now proud and haughty Galileo with 
the bitter feelings of disappointment and hate. 

The war was now openly declared, and waged with 
a fierceness which seems to have excited the mind of 
the young philosopher to the most extraordinary 
efforts. Driven from Pisa, by the numbers and influ- 
ence of his enemies, no suffering or danger could drive 
from his mind the great truths which his researches 
by experiment were constantly revealing. His spirit 
was unbroken, and in retiring from the unequal con- 
test, he hurled back defiance into the face of his con- 
quered, though triumphant persecutors. 

The mechanical investigations of Galileo, conducted 
with clearness and precision, soon led to the most 
important discoveries. He detected the law of falling 
bodies, and showed that the spaces described were 
proportional to the squares of the times ; that is, if a 
body fell ten feet in one second of time, it would fall 
four times as far in two seconds, nine times as far in 
three seconds, and so on for any number of seconds. 
He studied with success the subject of the composi- 
tion of forces, and demonstrated this remarkable pro- 
position, which lies at the very foundation of all 
modern mechanical philosophy. It may be thus stated. 
If a body receive an impulse, which singly would 



106 STRUCTURE OF THE UNIVERSE. 

cause it to move thirty feet in a second, on the line of 
the direction of the impulse, and at the same instant 
another impulse be communicated in a different direc- 
tion from the first, and which if acting alone would 
cause the body to move on the line of direction of the 
second impulse forty feet in one second, under the 
joint action of these two impulses the body will move 
in a direction easily determined from those of the 
impulsive forces, and will fly with a velocity of fifty 
feet in the first second of time. 

Such is the universal prevalence of this beautiful 
proposition, that no falling, flying, or moving body, 
whether it be the rifle ball, the cannon shot, or the 
circling planet, is free from its imperious sway. 
Strike the knowledge of this great truth from ex- 
istence, and the magnificent structure which modern 
science has reared, falls in ruins at a single blow. 
It is founded in the simple but invariable laws of 
motion, and while these endure, this elegant dis- 
covery of the Florentine philosopher will remain as 
a monument to his sagacity and penetration. 

Possessed of such rare qualities for philosophic 
research, so free from prejudice, and withal, so can- 
did, we cannot but inquire with interest, how the 
mind of Galileo stood affected towards the new 
astronomical doctrines of Copernicus. He had early 
adopted and taught the Ptolemaic system, and his con- 
version is so remarkable, and is so characteristic of 
the man, that it cannot be omitted. A disciple of 
Copernicus visited the city of Galileo's residence, and 
delivered several public lectures to crowded audi- 
ences, on the new doctrines. Galileo, regarding the 
whole subject as a species of solemn folly, would not 



LAWS OF MOTION AND GRAVITATION. 107 

attend. Subsequently, however, in conversing with 
one who had adopted these new doctrines, the Coper- 
nican sustained his views with such a show of rea- 
son that Galileo now regretted that he had heedlessly 
lost the opportunity of attending the lectures. To 
make amends, he sought every opportunity to con- 
verse with the Copernicans, and remarking that they, 
like himself, had all once been Ptolemaists, and that 
from the doctrines of Copernicus no one had ever 
subsequently become a follower of the old philosophy, 
he resolved to examine the subject with the most 
serious attention. The result may be readily antici- 
pated; the conversion was sudden and thorough, the 
old astronomy was abandoned, and the new convert 
became the great champion by whose ardor, and 
unconquerable zeal, the strongholds of antiquated 
systems were to be destroyed and a new and truthful 
one founded. 

Thus far the career of Galileo in science had been 
successful and brilliant. He was rapidly rising in 
reputation and influence, when a fortunate accident 
revealed to the world, the application of a principle 
in optics fraught with consequences, which it is im- 
possible to estimate. Galileo was informed that 
Jansen, of Holland, had contrived an instrument pos- 
sessing the extraordinary property of causing distant 
objects, viewed through it, to appear as distinctly as 
when brought near to the eye. The extensive knowl- 
edge which Galileo possessed of optics, immediately 
gave him the command of the important principle on 
which the new instrument had been constructed. He 
saw at once the high value of such an instrument in 



108 STRUCTURE OF THE UNIVERSE. 

his astronomical researches, and with his own hands 
commenced its construction. 

After incredible pains, he finally succeeded in con- 
structing a telescope, by whose aid, the power of the 
eye was increased thirty fold. It is impossible to con- 
ceive the intense interest with which the philosopher 
directed for the first time his wonderful tube to the 
inspection of the heavens. When we reflect that 
with the aid of this magical instrument the observer 
was about to sweep out through space, and to ap- 
proach the moon, and planets, and stars, to within a 
distance only one-thirtieth of their actual distance ; 
that their size was to increase thirty fold, and their 
distinctness in the same ratio, it is not surprising that 
these wonders should have excited the most extrava- 
gant enthusiasm. — Galileo commenced by an exami- 
nation of the moon. Here he beheld, to his inexpres- 
sible delight, the varieties of her surface clearly 
defined, her deep cavities, her lofty mountains, her 
extensive plains, were distinctly revealed to his aston- 
ished vision. Having satisfied himself of the reality 
of these inequalities of the moon's surface, by watch- 
ing the decreasing shadows of the mountains, as the 
sun rose higher and higher on the moon, he turned 
his telescope to an examination of the planets. These 
objects, which the human eye had never before beheld 
other than brilliant stars, now appeared round and 
clear and sharp, like the sun and the moon to unaided 
vision. On the 8th January, 1610, the telescope was 
for the first time directed to the examination of the 
planet Jupiter. Its disk was clearly visible, of a pure 
and silver white, crossed near the centre by a series 
of dark streaks or belts. Near the planet, Galileo 



LAWS OF MOTION AND GRAVITATION. 109 

remarked three bright stars which were invisible to the 
naked eye. He carelessly noted their position with 
reference to the planet, for he believed them to be 
fixed stars, and of no special interest, except to point 
out the change in Jupiter's place. On the following 
night, " induced," as he says, " by he knew not what 
cause," he again directed his attention to the same 
planet. The three bright stars of the preceding even- 
ing were still within the field of his telescope, but their 
positions with reference to each other were entirely 
changed, and such was the change, that the orbitual mo- 
tion of Jupiter could in no way account for it. Aston- 
ished and perplexed, the eager astronomer awaits the 
coming of the following night to resolve this mysterious 
exhibition. Clouds disappoint his hopes, and he is 
obliged to curb his impatience. — The fourth night was 
fair, the examination was resumed, and again the 
bright attendants of Jupiter had changed — his suspi- 
cions were confirmed — he no longer hesitated, and 
pronounced these bright stars to be moons, revolving 
about the great planet as their centre of motion. A few 
nights perfected the discovery; the fourth satellite was 
detected, and this astounding discovery was an- 
nounced to the world. 

No revelation could have been more important or 
more opportune than that of the satellites of Jupiter. 
The advocates of the Copernican theory hailed it with 
intense delight; while the sturdy followers of Ptolemy 
stoutly maintained the utter absurdity of such pre- 
tended discoveries, and urged as a sort of unanswera- 
ble argument, that as there were but seven openings 
in the head — two ears, two eyes, two nostrils and the 
mouth, there could be in the heavens but seven planets. 
K 



110 STRUCTURE OF THE UNIVERSE. 

The more rational, however, saw the earth, by this 
discovery, robbed of its pretended dignity. It com- 
manded the attendance of but one moon, while Jupiter 
received the homage of no less than four bright attend- 
ants. The delighted Copernicans saw in Jupiter as a 
central orb and in the orderly revolution of his satel- 
lites, a miniature of the sun and his planets, hung up 
in the heavens, and there placed to demonstrate to all 
coming generations, the truth of the new doctrines. 

Another discovery soon followed, which it is said 
the sagacity of Copernicus foresaw w r ould sooner or 
later be revealed to human vision. It had been urged 
by the Ptolemaists, that in case Venus revolved about 
the sun, as was asserted by Copernicus, and reflected 
to us the light of that luminary, then must she imitate 
exactly the phases of the moon ; when on the side oppo- 
site to the sun, turning towards us her illuminated hem- 
isphere she ought to appear round like the moon, while 
the crescent shape should appear on reaching the 
point in her revolution which placed her between the 
sun and the eye of the observer. As these changes 
were invisible to the naked eye, the objection was 
urged with a force which no argument could meet. 
Indeed it was unanswerable, and in case the telescope 
should fail to reveal these changes in Venus, the fate 
of the Copernican theory was forever sealed. 

The position of Venus in her orbit was computed — 
the crescent phase due to that position determined — 
the telescope applied, and the eye was greeted with 
an exquisite miniature of the new moon. There 
was the planet, and there was the crescent shape 
Jong predicted by Copernicus, received by him and 
his followers as a matter of faith, now become a 



LAWS Of MOTION AiND GRAVITATION. Ill 

matter of sight. The doctrines of Copernicus thus 
received not only confirmation, but so far as Venus 
was concerned, a proof so positive that no skepticism 
could resist. It is not my design to follow the dis- 
coveries of the Florentine philosopher among the 
planetary orbs. These will be resumed hereafter, 
when we come to examine more particularly the 
physical constitution of the planets. I have merely 
adverted to those discoveries, which became spe- 
cially important in the discussions between the par- 
tizans of the old and new astronomy. 

Admitting the doctrines of Copernicus, and uniting 
to them the great discoveries of Kepler, let us exam- 
ine the condition of astronomical science, ascertain 
precisely the point the mind had reached, and the na- 
ture of the investigations which next demanded its 
attention. From the first of Kepler's laws, the figure 
of the planetary orbits became known, and the mag- 
nitude of the ellipse described by any planet was easily 
determined. By observing the greatest and least dis- 
tances of any planet from the sun, the sum of these 
distances gave the longer axis of the orbit; and know- 
ing this important line, and the focus, it became a 
simple matter to construct the entire orbit. The line 
joining the planet with the sun, while the planet oc- 
cupied its shortest or perihelion distance, gave the 
position of the axis of the orbit in space, and its plane 
being determined by its inclination to that of the 
ecliptic, nothing remained to fix in space the figure, 
magnitude and position of the planetary orbits. The 
next point was to pursue and predict the move- 
ments of these revolving bodies. This was readily 
accomplished. A series of observations soon revealed 



112 STRUCTURE OF THE UNIVERSE. 

the time occupied by any planet in performing one 
complete revolution in its elliptic orbit. Knowing 
thus the periodic time, and the position of the planet 
in its orbit at any given epoch, the second law of 
Kepler furnished the key to its future movements ; its 
velocity in all parts of its orbit became known, and 
the mind swift and true followed the flying world in 
its rapid flight through space. It even went further; 
anticipated its changes, and predicted its positions, 
with a degree of certainty only limited by the accu- 
racy with which the elements of its orbit had been 
determined. 

The third of Kepler's laws, exhibiting the proportion 
between the periodic times and the mean distances of 
the planets from the sun, united all these isolated and 
wandering orbs into one great family. Their periods 
of revolution were readily determined by observation, 
and an accurate determination of the distance from 
the sun of a single planet in the group, gave at once 
the distances of all the remaining ones. The increased 
accuracy of the means of observation would render 
more perfect each successive measure of the earth's 
distance from the sun, and it seemed now that the 
mind might stop and rest from its arduous toil ; that 
scarcely any thing remained to be done. The solar 
system was conquered, and the fixed stars defied the 
utmost efforts of human power. 

How widely does this view differ from the true 
one. In fact, the true investigation had not even 
commenced. A height had indeed been gained, from 
whence alone the true nature of the next great prob- 
lem became visible, and standing upon this eminence 
the mind boldly propounds the following questions: — 



LAWS OF MOTION AND GRAVITATION. 113 

Why should the orbits of the planets and satellites be 
ellipses, rather than any other curve ? What power 
compelled them to pursue their prescribed paths with 
undeviating accuracy ? What cause produced their 
accelerated motion when coming round to those parts 
of their orbits nearer to the sun ? What power held 
planet and satellite steady in their swift career, pro- 
ducing the most exquisite harmony of motion, and a 
uniformity of results as steady as the march of time ? 

Here I may be asked, do not such questions border 
on presumption ? Are not such inquisitorial exami- 
nations touching on the domain of God's inscrutable 
providences, and would it not be wiser to stop and 
rest satisfied with the answer to all these questions, 
that God, w T ho built the universe, governs and sustains 
it by his power and wisdom ? Doubtless this answer 
is true, and in its truth man humbly finds his highest 
encouragement to attempt the resolution of the sub- 
lime questions already propounded for examination. 
Let us admit that the divine will produces all motion, 
speeds the earth in its rapid flight about the sun, 
guides the planets and their revolving moons, and 
poises the sun himself in empty space, as the great 
centre of life and light and heat to his attendant 
worlds. Is it not reasonable to believe that the will 
of the Omnipotent is exerted according to some uni- 
form system, that this system is law, and that this 
law is within the reach of man ? To encourage this 
view the simple laws of motion had been already 
revealed, and as these must exert a controlling influ- 
ence in our future examinations, we proceed to un- 
fold them. 

First, then, it was discovered that if any body, 
k2 



114 STRUCTURE OF THE UNIVERSE. 

situated in space and free to move, receive an impulse 
capable of giving it a velocity of ten feet in the first 
second of time, or any other velocity, it will move off 
in the direction of the impulse for ever in a straight 
line, and with undiminished and unchanged velocity. 
The intensity of the primitive impulse determines the 
velocity of the body which receives it, and the one is 
precisely proportioned to the other. Again, in case a 
moving body while pursuing its flight receives an im- 
pulse in a direction different from its primitive one, its 
new direction and velocity will be. determined by the 
direction and intensity of the new impulse, according 
to the principle discovered by Galileo, and already 
explained. Lastly, in every revolving body a dispo- 
sition is generated to fly from the centre of rotation. 
The body seems urged by some invisible force from 
the centre, and if the velocity be sufficiently in- 
creased, no matter how strong the bond which unites 
it to the centre, it will, in the end, be severed, and 
the body, freed from its centre, darts away in a 
straight line tangent to its former circle of revolu- 
tion. This power, which urges revolving bodies from 
the centre of motion, is called the centrifugal force, 
and is proportioned to the squares of the velocity of 
the revolving body. Hence a cord sufficiently strong 
to hold a heavy ball revolving round a fixed centre 
at the rate of fifty feet in a second, w T ould require to 
have its strength increased four fold, to hold the same 
ball, if its velocity should be doubled. 

These simple laws, derived from a rigorous exami- 
nation of those moving bodies, subject to man's closer 
scrutiny, extend their sway through the remotest re- 
gions of space. Are these laws necessary qualities 



LAWS OF MOTION AND GRAVITATION. 115 

of matter ? Why should a body, darting away under 
the action of some impulsive force, pursue forever its 
undeviating direction, with undiminished velocity ? — 
This effect cannot arise from any necessary property 
or quality of matter. The law might have been dif- 
ferent — the direction of the moving body might have 
slowly varied — the velocity might have increased or 
decreased in any proportion, and yet the flying body, 
so far as we can understand, have retained all its 
physical qualities and properties. No — Divine wis- 
dom has selected these simple and beautiful laws 
from among a multitude, either of which might have 
been chosen. Stretching forward, therefore, to the 
examination of the force by which the planets are 
retained in their orbits, was it not reasonable to 
expect, that some law might be found, governing 
the application of that mysterious power, and in 
some way proportioned to the mass of the moving 
body, and to the orbit which it described in wheeling 
around the sun. That they were held by some invisi- 
ble power to their centre of motion, was manifest 
from the fact that the centrifugal force, generated by 
the rapidity of their revolution, would have hurled 
them away from the sun, if not opposed and counter- 
poised by some equivalent power lodged in the great 
centre of the planetary orbs. Here was an object 
worthy the highest ambition of the human mind. — 
No matter what might be the nature of this force, 
whether it should reside in the sun, or in the planet, 
or in both — whether it should prove to be a property 
of matter, or the mere uniform manifestation of the 
Omnipotent will; the discovery of its law of action 
would give to the mind the power of penetrating the 



116 STRUCTURE OF THE UNIVERSE. 

darkest recesses of nature, and of rising to a knowl- 
edge of the profoundest secrets of the universe. 

Such is the nature of the investigation propounded 
to the powerful intellect of Newton. This eminent 
philosopher, justly regarded as the most extraordinary 
genius that ever lived, neither originated the question 
which he undertook to discuss, nor divined the law 
of force which he proposed to demonstrate. When 
Kepler had closed the investigations which led to the 
discovery of his three great laws, his sagacity at once 
suggested to his mind the existence of some central 
force, by whose power the planetary movements were 
controlled. He had watched the moon circling around 
the earth, he had scrutinized the ocean tide, whose 
crested wave seemed to rise and follow the move- 
ments of the moon, until he boldly announced that 
some invisible bond, some inscrutable power, united 
the one to the other. He even reached the conclu- 
sion, that this unknown force resided in the moon — 
that by its power the waters were heaved from their 
beds, and caused to follow the moon and imitate its 
motions. Doubtless the solid earth itself felt this 
mysterious power, and swayed to its influence ; but in 
consequence of the immobility of its particles, its 
effects had, thus far, escaped detection. Thus once 
started on the track, Kepler pursued the speculation. 
He attributed a similar power to the sun, and exten- 
ded its controlling influence to the planets. He went 
yet farther, and conjectured that the law of this un- 
known force was such that it diminished as the squares 
of the distances at which it operated increased. That 
is, if the intensity of the power which it exerted on 
a planet where the distance was one hundred millions 



LAWS OF MOTION AND GRAVITATION. 117 

of miles from the sun, be counted as unity, removing 
the planet to double the distance, or to two hundred 
millions of miles, the sun's influence over it would be 
reduced to one-fourth of its former value. 

With Kepler this wonderful conjecture always re- 
mained without proof. He had placed it on record, 
and succeeding philosophers had treated it with 
greater or less seriousness, according to the esti- 
mate which they placed upon the sagacity of its 
author. Even if Kepler, himself, had attempted the 
demonstration of this principle — the data were as 
yet wanting, which would have rendered its accom- 
plishment possible. The period intervening between 
the time of Kepler and Newton had not been left 
unimproved. Descartes had revealed the law of 
centrifugal force, and by one of those extraordinary 
strokes of genius — occurring once in an age — had 
fastened the irresistible power of analysis upon 
geometry, which had given to the mind a force and 
rapidity in the investigation of the figure of curves 
and curvilinear motion, which had quadrupled its 
capacity. By repeated efforts, a more accurate knowl- 
edge had been obtained of the circumference and 
diameter of our earth, and through this the distance 
of the moon from the earth in the successive points 
of its orbit had been approximated with still greater 
precision. 

With these advantages, Newton gave the energies 
of his mind to the demonstration of that principle 
which had existed. with Kepler as a mere conjecture. 

Before proceeding to develop the train of reason- 
ing pursued by the great English astronomer, permit 
me first to prepare the way by a simple and per- 



118 STRUCTURE OF THE UNIVERSE. 

spicuous exhibition of the method employed in deter- 
mining the diameter of the earth and the distance of 
the moon ; two elements which figure conspicuously 
in the demonstration about to be made, and without a 
knowledge of which it would have been impossible to 
proceed. We commence with a determination of the 
diameter of the earth. 

If an observer should start from any point on the 
surface of the earth in the northern hemisphere, and 
fixing his eye upon the north pole of the heavens, 
should travel directly towards that point, all the stars 
in the north would appear to rise higher above the 
horizon as he advanced in his journey. The star 
which occupied the point immediately above his 
head when he started, would appear gradually to de- 
cline towards the south. If it were possible to travel 
on the same great circle of the earth entirely around 
its circumference, the zenith star would appear to 
pursue an opposite route in the heavens, and would 
return to its primitive position only on the return of 
the observer to his point of starting. This, however, 
is not possible. What the observer can accomplish, 
is this. He may travel north until his zenith star 
shall appear to have moved south by one degree, or 
the three hundred and sixtieth part of the circumfer- 
ence of the heavens ; then will he have passed over 
the three hundred and sixtieth part of the entire cir- 
cumference of the earth ; all these parts are of equal 
length, — he measures the one over which he has 
passed — multiplies its value by ♦three hundred and 
sixty, and the result gives him the circumference of 
the earth, from which the diameter is readily deduced 
by the well-known proportion which exists between 



LAWS OF MOTION AND GRAVITATION. 119 

these lines. By this simple method, the diameter of 
the earth being determined, its radius is known, and 
we are prepared to explain the process by which the 
moon's distance may be found. 

Let us locate, in imagination, two observers at 
distant points on the same great circle of the earth, 
each prepared to measure the angular distance at which 
the moon appears from the zenith point of each sta- 
tion ; but the zenith of any place is the point in which 
the earth's radius prolonged reaches the heavens, — 
the angular distance of the moon from the zenith will 
exhibit precisely the inclination of the visual ray 
drawn to the moon's centre with the earth's radius 
drawn to the place of observation ; the zenith dis- 
tances being observed at each station, the observers 
knowing that part of the great circle of the earth by 
which their stations are separated, come together, 
compare observations, and construct a figure composed 
of four lines. Two of these are the radii of the earth 
drawn to the points of observation. These may be 
laid down under their proper angle, — drawing from 
their extremities two lines, forming with the radii, an- 
gles equal to the moon's measured zenith distances. 
These represent the visual rays drawn to the moon; 
they meet in a point which determines their length, 
and if the figure be constructed accurately, it will be 
found that either of these lines is about sixty times 
longer than the radius of the earth, or the moon's dis- 
tance is about 240,000 miles. 

We now return to the examination of the great 
question of a central force, and to the discovery of its 
law of action. Allow me in the out-set to explain, 
with extreme simplicity, the assumed law, whose 



120 STRUCTURE OF THE UNIVERSE. 

truth or falsehood it was required to demonstrate. If 
any force resided in the sun which could resist the 
centrifugal force of the planets, or in any primary to 
resist the centrifugal force of the revolving satellite, 
it was conjectured that this force would decrease in 
proportion as the square of the distance increased. 
In other language, if the planets were arranged at 
the following distances from the sun, the forces exert- 
ed upon them would be represented by the second 
series, thus : 

Distances, 12 3 4 5 6 &c, 

Forces, 1 £ i ft ft ft &c. 

The measure of the intensity of any force of attrac- 
tion situated at the centre of the earth or sun, is 
accurately represented by the velocity it is capable of 
imparting to a falling body in any unit of time. Ex- 
periment shows that that power which causes a heavy 
body to fall to the earth's surface, is capable of im- 
pressing upon it a motion of about 16 feet in the first 
second of time after its fall commences. In case the 
force diminishes, as we remove the falling body 
farther from the centre of attraction, the law of 
diminution would manifest itself in the- diminished 
amount of motion communicated to the falling body. 

Now if Newton could have carried a heavy body 
upward, above the earth, until he should gain a height 
above its surface of four thousand miles, he w r ould 
then be twice as far from the centre as when at the 
surface of the earth. Dropping the heavy body, and 
measuring accurately the distance through which it 
passes in the first second of time, in case he finds 
this to be one-fourtli of 16 feet, the distance fallen 
through by the same body in the same time, at the 



LAWS OF MOTION AND GRAVITATION. 121 

distance of 4000 miles from the earth's centre, the 
result would have confirmed the law which conjecture 
had assigned as the law of nature. Could he have 
mounted one unit higher, gaining an altitude of 8000 
miles above the earth's surface, or three units from 
the centre, here repeating his experiment, in case the 
space passed through by the falling body is now one- 
ninth of 16 feet, it would yet farther confirm the truth 
of the conjectured law. Thus, could he have increased 
his altitude by one unit or radius of the earth after 
another, repeating his experiment as each new unit 
was added to his elevation, finding in every instance 
the law of diminution fulfilled by the falling body, all 
doubt as to the truth of the law would have been 
removed, and its foundation in nature would have 
justly flowed from such a series of experiments. 

Here, then, is precisely what must be accomplished 
to demonstrate the assumed law of gravitation. But 
since these altitudes of 4000 and 8000 miles could not 
be reached, might not some change in the distance 
passed over by a heavy falling body, be noticed and 
measured, if removed from a valley to the top of the 
highest mountain? Alas ! the increased distance from 
the centre of the earth, gained by ascending the loftiest 
mountain on its surface, is almost inappreciable, 
when compared with the entire distance, four thou- 
sand miles. Even if the mountain were ten miles 
high, the two elevations at which the experiment 
might then be performed, would be 4000 miles and 
4010 miles, and the diminished velocity would not be 
appreciable, even with the most delicate tests, much 
less could it be relied on to demonstrate the truth or 
falsehood of a great principle. Here, then, the mind 
L 



122 STRUCTURE OF THE UNIVERSE. 

was brought to a full stop ; and for a long time it 
seemed impossible that the philosopher should con- 
quer the difficulties which rose up in his path, and 
defied his further advance. Finding it impossible 
to perform any satisfactory experiment on the earth's 
surface, the daring mind of Newton conceived the 
idea of employing the moon itself as the falling body, 
and of testing the truth of his great theory by its fall 
towards the earth. But could he reach out his hand, 
grasp the revolving moon, stop it in its orbit, drop it 
to the earth, and measure its descent in the first sec- 
ond of time ? No — this was impossible. The moon 
could not be arrested in its career ; but is this neces- 
sary ? Is not the moon, in one sense, constantly fall- 
ing towards the earth ? Newton asserted this to be 
true, and thus did he prove it. 

Stand upon the earth, and stretching outward into 
space 240,000 miles, there let the moon be located, 
poised and fixed in space, on a point of its present 
orbit. There let us suppose it to receive an impulse in 
a direction perpendicular to the line which joins it 
with the earth. By the first law of motion, being 
free to move, it will sweep off in a straight line, tan- 
gent to its present orbit, and will pass over a space 
in the first second of time, proportioned to the inten- 
sity of the impulse received. Mark that space, and 
bring the moon back to its primitive position. Now 
drop it towards the earth, and as it descends freely 
under the earth's attraction, mark the space through 
which it falls in the first second of time. This being 
known, bring back the moon once again to its starting- 
point. Now combine the impulsive force first given, 
with that power which caused the moon, when left 



LAWS OF MOTION AND GRAVITATION. 123 

free to move, to fall to the earth. Let them both act 
at once : the impulse is given, the moon darts off in 
a straight line, but is instantly seized by the earth's 
attraction, which drags it from its rectilineal path, 
and the two contending forces, ever struggling, neither 
conquering, exercise a divided empire over the 
moon ; onward she moves, obedient to the impulsive 
force, bent to her orbit by the action of the earth's 
attraction. Now the amount by which it is deflected 
in one second of time, from the straight line it would 
have pursued, is the amount precisely, by which it falls 
to the earth. 

If thus far I have been successful, what remains 
can readily be accomplished. Newton easily compu- 
ted, from the known velocity of the moon in its orbit, 
and from the radius of that orbit, the space through 
which the moon actually fell towards the earth in one 
second of time. He next computed the space through 
which a heavy body would fall towards the earth's 
surface, if removed from the earth to a distance equal 
to that of the moon. Now in case these two quantities 
should prove to be exactly equal, the truth of the 
demonstration would be complete ; the moon did fall 
through the space required by the assumed law, and 
in this event the law must be the law of nature. For 
seventeen long years did this incomparable philoso- 
pher, rivaling the example of the immortal Kepler, 
toil on in this most difficult enterprise. He finally 
reaches the result; the two quantities are found and 
compared, but alas ! the computed distance through 
which the moon must fall, in case the law of gravita- 
tion were true, differed from the observed distance 
through which it actually fell, by a sixth part of its 



124 STRUCTURE OF THE UNIVERSE. 

value. Any less scrupulous, any less philosophic 
mind, would have been content with this near approx- 
imation, and would have announced the discovery to 
the world. Not so with Newton. Nothing short of 
the most rigorous accuracy could satisfy his consci- 
entious regard for truth. His manuscripts are laid 
aside, and the pursuit for the present abandoned. 

Months roll by. Occasionally he returns to his 
computations, runs over the figures, hoping to detect 
some numerical error ; but all is right, and he turns 
away. At length, while attending a meeting of the 
Royal Society in London, he learns that Picard had just 
closed a more accurate measurement of the diameter 
of the earth. This was one of the important quanti- 
ties which entered into his investigation. He returns 
home, — and with impatient curiosity spreads before 
him his old computations — the new value of the earth's 
diameter is substituted — he dashes onward through 
the maze of figures — he sees them shaping their 
values towards the long sought result — the excitement 
was more than even his great mind could bear — he 
resigns to a friend — the work is completed, the results 
compared — they are exactly equal ! The victory is 
won, — he had seized the golden key which unlocks 
the mysteries of the universe, and he held it with a 
giant's grasp ! 

There never can come another such moment as the 
one we have described, in the history of any mortal. 
There are no such conquests remaining to be made. 
Standing upon the giddy height he had gained, 
Newton's piercing gaze swept forward through 
coming centuries, and saw the stream of discovery 
flowing from his newly discovered law, slowly increas- 



LAWS OF MOTION AND GRAVITATION. 125 

ing, spreading on the right hand and on the left, 
growing broader, and deeper, and stronger, encircling 
in its flow planet after planet, sun after sun, system 
after system', until the universe of matter was encom- 
passed in its mighty movement. He could not live to 
accomplish but a small portion of this great work. — 
Rapidly did he extend his theory of gravitation to the 
planets and their satellites. Each accorded perfectly 
with the law, and rising as the inquiry was pursued, 
he at length announced this grand prevailing law : 

Every particle of matter in the universe attracts every 
other particle of matter with a force or power directly 
proportioned to the quantity of matter in each, and decreas- 
ing as the squares of the distances which separate the 
particles increase. 

Having reached this wonderful generalization, 
Newton now propounded this important inquiry. 
" To determine the nature of the curve which a body 
would describe in its revolution about a fixed centre, 
to which it was attracted by a force proportional to 
the mass of the attracting body, and decreasing with 
the distance according to the law of gravitation." 

His profound knowledge of the higher mathematics, 
which he had greatly improved, gave to him aston- 
ishing facilities for the resolution of this great problem. 
He hoped and believed that when the expression 
should be reached, which would reveal the nature of 
the curve sought, that it would be the mathemat- 
ical language descriptive of the properties of the 
ellipse. This was the curve in which Kepler had 
demonstrated that the planets revolved, and a confirm- 
ation of the law of gravitation required that the ellipse 
l 2 



126 STRUCTURE OF THE UNIVERSE. 

should be the curve described by the revolving body, 
on the conditions announced in the problem. 

There happens to be a remarkable class of curves, 
discovered by the Greek mathematicians, called the 
conic sections; thus named, because they can all be 
formed by cutting a cone in certain directions. The 
figure of a cone with a circle for its base, and converg- 
ing to a point, is familiar to all. Cut this cone 
perpendicular to its axis, remove the part cut, and 
the line on the surface round the cone will be found 
to be a chicle. Cut it again, oblique to the axis, then 
the line of division of the two parts will be an ellipse. 
Cut again so that the knife may pass downward 
parallel to the slope of the cone, and in this case 
your section is a parabola. Make a last cut parallel 
to the axis of the cone, and the curve now obtained 
is the hyperbola. 

When Newton reached the algebraic expression 
which, when interpreted, would reveal ihe proper- 
ties of the curve sought and which he had hoped 
would prove to be the ellipse — he was surprised to 
find that it did not look familiar to his eye. He ex- 
amined it closely — it was not the equation of the 
ellipse, and yet it resembled it in some particulars. 
What was his astonishment to find, on a complete 
examination, that the mathematical expression, which 
he had reached, expressing the nature of the curve 
described by the revolving body, was the general 
algebraic expression embracing all the conic sections. 
Here is a most wonderful revelation. Is it possi- 
ble that under the law of gravitation, the heavenly 
bodies may revolve in any or either of these curves ? 
Observation responds to the inquiry. The planets 



LAWS OF MOTION AND GRAVITATION. 127 

were found to revolve in ellipses; the satellites of 
Jupiter in circles; and those strange, anomalous, out- 
lawed bodies, the comets^ whose motions hitherto 
had defied all investigation, take their place in the 
new and now perfect system, sweeping round the sun 
in parabolic and hyperbolic orbits. 

Thus were these four beautiful curves, having a 
common origin, possessed of certain common proper- 
ties, yet diverse in character, mingling in close prox- 
imity, and gliding imperceptibly into each other, sud- 
denly transferred to the heavens, to become the orbits 
of countless worlds. For nearly twenty centuries, 
they had been the objects of curious speculation to 
the mathematician ; henceforward they were to be 
given up to the hands of the astronomer, the power- 
ful instrument of his future conquests among the 
planetary and cometary worlds. 

The three great laws of Kepler, to which he had 
risen with such incredible toil and labor, were now 
found to flow as simple consequences of the law of 
gravitation. It is impossible to convey the slightest 
idea, in discussions so devoid of mathematics, of the 
incredible change which had thus suddenly been 
wrought in the mode of investigation. I never have 
closed Newton's investigation, by which he deduces 
the nature of the curve, described by a body revolving 
around a fixed centre, under the law of gravitation, 
bearing with it consequences so simple yet so wonder- 
ful, without feelings of the most intense admiration. I 
can Convey no adequate idea of the difference of the 
methods employed by Kepler and Newton, in reach- 
ing the three laws of planetary motion. J see Kep- 
ler in the condition of one on whom the fates have 



128 STRUCTURE OF THE UNIVERSE. 

fixed the task of rolling a huge stone up some rug- 
ged mountain side, to its destined level, within a few 
feet of the summit. He toils on manfully, heav- 
ing and struggling, day and night, in storm and in 
darkness, never quitting his hold, lest he may lose 
what he has gained. If the ascent be too steep and 
rocky, he diverges to the right, then to the left, wind- 
ing his heavy way zigzag up the mountain side. — 
Years glide by — he grows gray in his toil, but he never 
falters — onward and upward he still heaves the heavy 
weight — his goal is in sight, he renews his efforts, the 
last struggle is over — he has finished his task — the 
goal is won. 

Such was Kepler's method of reaching his laws. 
Now for Newton's. He stands, not at the base 
of the mountain, with its long, ascending rocky sides, 
but on the top. He starts his heavy stone, it rolls of 
itself over, slowly over, and once again, and falls qui- 
etly to its place. Let me not be misunderstood in 
this strange comparison, as detracting in the smallest 
degree from the just fame that is due to Kepler. But 
for his sublime discoveries, Newton could never have 
reached the mountain summit, on which he so proudly 
stood. Standing there, he never forgot by whose 
assistance he had reached the lofty point, and ever 
recognized, in the most public manner, his deep 
indebtedness to the immortal Kepler. 

A few words with reference to the rigorous appli- 
cation of Kepler's laws in nature, will close this dis- 
cussion. The first law, announcing the revolution of 
the planets in elliptic orbits, was now made general, 
and recognised the revolution of the heavenly bodies 



LAWS OF MOTION AND GRAVITATION. 129 

in conic sections : the circle, ellipse, parabola and 
hyperbola. 

The second law, fixing the equality of the spaces 
passed in equal times, by the lines joining the planets 
to the sun as these were carried round in their elliptic 
orbits, now became applicable to all bodies revolving 
about a fixed centre, in any curve, and according to 
any law. 

The third law, recognising the proportion between 
the squares of the periodic times and the cubes of 
the mean distances of the planets, was extended to 
the satellites, and to the comets ; modified slightly in 
the case of the larger planets, by taking into account 
their masses or quantities of matter. 

Here we close the era of research by observation. 
The mind has gained its last grand object. The era 
of physical astronomy dawns ; new and wonderful 
scenes open, and to the contemplation of these, we 
shall soon invite your attention. 



LECTURE V. 

UNIVERSAL GRAVITATION APPLIED TO THE EXPLANATION 
OF THE PHENOMENA OF THE SOLAR SYSTEM. 

The progress of the mind, in its efforts to reach a 
satisfactory explanation of the movements of the 
heavenly bodies, previous to the discovery of univer- 
sal gravitation, had been made independent of any 
guiding law. The mind had been feeling its way 
slowly and laboriously, guiding its direction by atten- 
tively watching the celestial phenomena, and relying 
for its success exclusively on the accuracy and num- 
ber of its observations. Each discovery made was 
isolated, and although it prepared the way for the 
succeeding ones, it did not in any sense involve them 
as necessary consequences. By the discovery of the 
great law of universal gravitation, a perfect and 
entire revolution had been made in the science of 
astronomy. A new department was now added, 
which, previous to the knowledge of this law, could 
have no existence. In this branch of astronomy, the 
process of investigation being inverted, the mind de- 
scends from one great law to an examination of its 
consequences, tracing these in their modified and 
diversified influences to their final limits. Observa- 
tion is now employed to verify discovery, and not 
as the basis on which, and without which, discovery 
cannot be madje. 

t 131 1 



132 STRUCTURE OF THE UNIVERSE. 

The era of physical astronomy is, therefore, the 
great era in the history of the science. It involves 
the resolution of the most wonderful problems — it 
calls into use the most refined and powerful mathe- 
matical analysis, and demands the application of the 
most ingenious and delicate instruments in seeking for 
the data by means of which its theory may be rendered 
practically applicable to the problems of nature. 
The mechanical philosopher in his closet may con- 
struct his imaginary system. In its centre he locates 
a sun, containing a certain mass of matter. — At any 
convenient distance from this sun he locates a planet, 
whose weight he assumes. To this planet he gives 
an impulse, whose intensity and direction are assumed. 
The moment these data are fixed, and the impulse 
given to the imaginary planet — no matter in what 
kind of an orbit it may dart away, whether circular, 
elliptical, parabolic, or hyperbolic — the laws of motion 
and gravitation asserting their empire, the planet is 
followed by the mathematician, with a certainty and 
accuracy defying all escape. He assigns its orbit in 
the heavens — the velocity of its movement — the pe- 
riod of its revolution. In short, in a single line, he 
writes out its history with perfect accuracy for a mil- 
lion years. 

If, now, to this simple system of a great central sun 
and one solitary planet, the physical astronomer add 
a third body, a moon, to the planet, he assumes its 
weight, the intensity and direction of the impulsive 
force starting it in its career, and now his system be- 
comes more complex. Strike the sun out of exist- 
ence, fix the planet, and the process of binding the 
satellite in mathematical fetters is precisely similar 



UNIVERSAL GRAVITATION. 133 

to that by which the movements of the planet were 
prescribed around the sun before the existence of the 
satellite. But now, with these three bodies the train of 
investigation becomes more intricate and involved. 
While the planet alone circulated around the sun, 
such is the undeviating accuracy with which it will 
forever pursue its path around the sun, that if it were 
possible to hang up in space along its route golden 
rings, whose diameter would just permit the flying 
planet to pass, millions of revolutions will never 
mark the slightest change. The rings once passed 
and then fixed, will mark forever the pathway of the 
solitary planet. But the moment a moon is given to 
this flying world, in that instant its motion is changed — 
it is swayed from its original fixed orbit — it no longer 
passes through the golden rings, and although the 
physical astronomer may write out in his analytic 
symbols the future history of his planet and moon, 
these expressions are no longer marked w r ith the sim- 
plicity which obtained in those which recorded the 
history of the single planet. While solitary, all 
changes w r ere effected by the planet in one single 
revolution, and these were repeated in the same pre- 
cise order in each successive revolution. Now, with 
the satellite added, there are changes introduced run- 
ning through many revolutions, and requiring for 
their complete compensation vast periods of time. 
Indeed, the inquiry arises, whether this system of a 
central sun, with a planet and its satellite revolving 
about it, can be so constituted that the changes 
which the planet and its moon mutually produce on 
each other's movements, may not go on, constantly 
accumulating in the same direction, until all features 
M 



134 STRUCTURE OF THE UNIVERSE. 

of the original orbits of both may be destroyed, both 
worlds being finally precipitated on the sun, or driven 
farther and farther from this luminary, until they 
are lost in infinite space. This inquiry, in a more 
extended form, will be examined hereafter. We pro- 
ceed to build up our imaginary system. Thus far, 
we have regarded our planet and its satellite as mere 
material heavy points. In case we give to them mag- 
nitude and rotation on an axis, the velocity of rota- 
tion will determine the figure of the planet and of its 
satellite. These figures will deviate from the exact 
spherical form, and this change of figure will sensibly 
affect the stability of the axis of rotation, and will 
introduce a series of subordinate movements, each of 
which must become the subject of research; and to 
write out the future history of the system, these mi- 
nute and concealed changes must likewise receive 
their mathematical expression. 

Having thus thoroughly mastered all the phenom- 
ena of this system of three bodies, the astronomer 
now adds another planet, whose mass is assumed, to- 
gether with the direction and intensity of its primi- 
tive impulse. Its orbit is now computed, subject to 
the greatly predominant influence of the sun, but sen- 
sibly affected by the quantity of matter in the old 
planet and its satellite, which prevents it from form- 
ing a fixed and unchangeable orbit in space. Again 
he is obliged to return to an examination of his first 
planet and its moon, for these again break away from 
their previous routes, and in consequence of the ac- 
tion of the second planet, assume new orbits, and are 
subjected to periodical fluctuations, which demand 
critical examination, and without a knowledge of 



UNIVERSAL GRAVITATION. 135 

which no truthful history of the planetary system can 
be written. To the second planet let us now add 
several satellites, each of which has its mass as- 
signed, and the direction and intensity of the impul- 
sive force by which they are projected in their orbits. 
Here, then, is a subordinate system demanding a 
complete examination. The satellites mutually af- 
fect each other's motions, and each is subjected to the 
influence of the primitive planet and its moon. Again 
does the physical astronomer review his entire inves- 
tigation. The addition of these satellites to his second 
planet has introduced changes in all the previous 
bodies of the system, which must now be computed, 
to keep up with the growing complexity. This task is 
at last accomplished. All the changes are accurately 
represented. Analysis has mastered the system, and 
the history of its changes are written out for hun- 
dreds and thousands of years. 

A third planet, with its satellite, is now added. 
This new subordinate system is discussed, and its op 
eration on all the previous planets and satellites com- 
puted, and after incredible pains, the astronomer once 
more masters the entire group, and follows them all 
with unerring precision, through cycles of changes 
comprehending thousands or even millions of years. 

Thus does the difficulty of grasping the system in- 
crease in a high ratio by the addition of ever)* new 
planet and satellite, till finally the last one is placed 
in its orbit, and the system is complete, so far as 
planets and satellites are concerned. Through this 
complicated system now cause thousands of comets to 
move in eccentric orbits, coming in from every quarter 
of the heavens, plunging downwards towards the sun, 



136 STRUCTURE OF THE UNIVERSE. 

sweeping with incredible velocity around this central 
luminary, and receding into space to vast distances, 
either to be lost forever, or to return after long peri- 
ods to revisit our system. These wandering bodies 
must be traced and tracked, their orbits fixed, their 
periods determined, their influence on the planets and 
satellites, and that exerted by these on the comets, 
must be computed and determined; then, and not till 
then, does the physical astronomer reach to a full 
knowledge of this now almost infinitely complex 
system. 

In this imaginary problem it will be observed that 
certain quantities were invariably assumed before the 
discussion could proceed. The mass of the sun — the 
mass of each planet and satellite — the intensity and 
direction of the primitive impulse given to each planet 
and satellite — these quantities are supposed to be 
known. If, now, the astronomer has actually ac- 
complished the resolution of the imaginary problem, 
and has obtained analytic expressions which write 
out and reveal the future history of his assumed 
planets and satellites, as they revolve around his as- 
sumed sun, if in these expressions he should substi- 
tute the actual quantities which exist in the solar 
system for those assumed, his expressions would then 
give the history of the solar system for coming ages, 
and by reverse action would reveal its past history 
with equal certainty. 

Before we can, therefore, bring the power of analy- 
sis to bear on the resolution of the grand problem 
of nature, we must interrogate the heavens, and ob- 
tain the absolute weight of our sun, of each planet, 
and of every satellite. Next we require the intensity 



UNIVERSAL GRAVITATION. 137 

and direction of the impulsive force which projected 
each planet and satellite in its orbit, and which would 
have fixed forever the magnitude and position of that 
orbit, in case no disturbing causes had operated to 
modify the action of the primitive impulse. 

Having thus attempted to exhibit, at a single view, 
the general outlines of the great problem of the solar 
system, we propose now to return to the examination 
of a system composed of three bodies ; and to fix our 
ideas, we assume the sun, earth, and moon. In case 
the earth existed alone, the elliptic orbit described in 
its first revolution around the sun would remain un- 
changed forever, and having pursued it, and marked 
its changes of velocity in the different parts of its 
orbit for a single revolution, this would be repeated 
for millions of years. But let us now give to the 
earth its satellite, the moon, and setting out from its 
perihelion, or nearest distance from the sun, let us 
endeavor to follow these two bodies as they sweep 
together through space, and mark particularly the 
effect produced on the moon's orbit by the disturbing 
influence of the sun. To give to the problem greater 
simplicity, let us conceive the plane of the moon's 
orbit to coincide with the earth's. The law of gravi- 
tation which gives to every attracting body a power 
over the attracted one, gravity increasing as the dis- 
tance decreases, it will be perceived that when the 
earth and moon are nearest to the sun, whatever in- 
fluence the sun possesses to embarrass or disturb the 
motions of the moon about the earth, will here be ex- 
ercised with the greatest effect. But since the sun is 
exterior to the moon's orbit, its tendency will be to 
draw the moon away from the earth, and cause her 



138 STftUCTUflE OF TilE UNIVERSE. 

to describe around her primary a larger orbit, in a 
longer period of revolution than would have been 
employed in case no sun existed, and the moon was 
given up to the exclusive control of the earth. 

Starting the planet on its annual journey, as it 
recedes from the sun in passing from its nearest to its 
most remote distance, or from perihelion to aphelion, 
the moon is gradually removed from the disturbing 
influence of the sun; it is subjected more exclusively 
to the earth's attraction ; its distance from the earth 
grows less, and the periodic time becomes shorter. 
These changes continue in the same order until the 
earth reaches its aphelion. There the moon's orbit 
is a minimum, and its motion is swiftest. In passing 
from the aphelion to the perihelion, the earth is con- 
stantly approaching the sun, and as the sun's influ- 
ence on the moon increases as its distance diminishes, 
its orbit will now expand by slow degrees, and the 
periodic time will diminish until on reaching the peri- 
helion, in case the figure of the earth's orbit remains 
unchanged, the moon's periodic time will be restored 
to its primitive value, and all the effects resulting 
from the elliptic figure of the earth's orbit will have 
been entirely effaced. 

Thus far we have directed our attention exclusively 
to the changes in the distance of the moon and its 
periodic time. But the moon's orbit is elliptical, as 
well as the earth's, and it is manifest that the sun's 
influence will operate to change not only the magni- 
tude of this orbit, but will in like manner produce a 
change in the position of the moon's perigee, or nearest 
point of distance from the earth. If the earth were 
stationary, and the moon revolved around it, passing 



UNIVERSAL GRAVITATION. 139 

between it and the sun, and then coming round so as 
to be beyond the earth with respect to this luminary, 
although the moon's orbit would be sensibly affected 
by the sun's attraction, yet this having exerted itself 
during one revolution of the moon, all its effects 
would be repeated in the same order during the next 
revolution, and the relative positions of the sun and 
earth remaining the same, the moon w T ould come 
finally to have a fixed orbit, and its principal lines or 
axes would never change. But this is not the case 
of nature. — The earth swiftly turning in its orbit, and 
bearing with it its revolving satellite, by the time the 
moon has completed a revolution, the sun and earth 
have entirety changed their relative positions, and 
the moon cannot reach its perigee, or nearest distance 
from the earth, at the same point as in the preceding- 
revolution. 

By an attentive examination of this problem, it is 
found that the tendency is to cause the moon to reach 
its perigee earlier than it would do if not disturbed, 
and in this way the perigee of a fixed orbit appears 
to advance to meet the coming moon, and in the end 
to continue advancing until it actually revolves en- 
tirely round in a period which observation determines 
to be about nine years. 

It is not my intention to enter into a detailed ex- 
amination of all the effects resulting from the sun's 
disturbing power on the moon's motions ; neither shall 
I attempt to exhibit all the effects produced by the 
moon on the earth. — This would require a train of 
investigation too elaborate and intricate to comport 
with my present purposes. My object is simply to 
show that changes must arise from the mutual and 



140 STRUCTURE OF THE UNIVERSE. 

reciprocal action of these three bodies, which the 
theory of gravitation must explain, and the telescope 
point out, before it be possible to obtain a perfect 
knowledge of these bodies. 

The exact estimation of these changes can never 
be made until we shall have learned the relative 
masses of matter contained in the sun, earth, and 
moon. In other language, w T e must know how many 
moons it would require to weigh as much as the 
earth, and how many earths would form a weight 
equal to that of the sun. 

But is it possible that man, situated upon our planet, 
237,000 miles from the moon, and 95,000,000 of miles 
from the sun, can actually weigh these worlds against 
each other, and determine their relative masses of 
matter ? Even this has been accomplished, and I shall 
now proceed to explain how the earth may be weighed 
against the sun. Dropping a heavy body at the earth's 
surface, the velocity impressed on it in the first second 
of time will measure the weight of the earth in one 
sense. If it were possible to take the same body to 
the sun, drop it, and measure the velocity acquired by 
the falling body in the first second of time, the rela- 
tive distances passed through at the sun and at the 
earth by the same body in the same time, would 
show exactly the relative weight of the sun and 
earth, for their capacity to communicate velocity are 
exactly proportioned to their masses. Now, although 
this experiment cannot be performed in the exact 
terms announced, yet as we have already shown, the 
moon is constantly dropping towards the earth, and 
the earth is as constantly dropping towards the sun. 
Now in case we measure the amount by which the 



UNIVERSAL GRAVITATION. 141 

moon is deflected from a straight line in one second 
of time, this measures the intensity of the earth's 
power. But the amount by which the earth is de- 
flected from a right line by the central power of 
the sun in one second, is easily measured from a 
knowledge of its period and the magnitude of its or- 
bit. Executing these calculations, it is found that the 
sun's effect on the earth is rather more than twice as 
great as the earth's effect on the moon, and in case 
these effects were produced at equal distances, then 
would the sun be shown to contain rather more than 
twice as much matter as is found in the earth. But 
the sun produces its effect at a distance 400 times 
greater than that at which the earth acts on the 
moon : hence, as the force diminishes as the square 
of the distance increases, a sun acting at twice the 
distance at which the earth acts, must be four times 
heavier to produce an equal effect ; at three times 
the distance, it must be nine times heavier, and at 
four times the distance, sixteen times heavier ; — at 
400 times the distance, 160,000 times heavier than the 
earth. Thus do we find that in case the sun's action 
on the earth were exactly equal to the earth's action 
on the moon, in consequence of the great distance at 
which it operates, its weight would be equal to that 
of 160,000 earths. But its actual effect is rather 
more than double that of the earth on the moon, and 
hence we find it contains rather more than double 
160,000 earths, or exactly 354,936 times the quantity 
of matter contained in the earth. 

This enormous mass of the sun is confirmed by 
an examination of its actual dimensions. An object 
with an apparent diameter equal to that of the sun, 



142 STRUCTURE OF THE UNIVERSE. 

and at a distance of 95,000,000 of miles, must have a 
real diameter of 883,000 miles, a quantity so great 
that if the sun's centre were placed at the earth's 
centre, its vast circumference would give ample room 
for the moon to circulate within its surface, leaving 
as great a space between the moon's orbit and the 
sun's surface as now exists between the moon and 
earth. 

It is this immense magnitude of the sun, when 
compared with the planets and their satellites, which 
renders the orbits of the planets comparatively unal- 
terable. It is true that these bodies mutually affect 
each other, but these effects are comparatively slight, 
and astronomers regard them as perturbations, or mere 
disturbances of the original elliptic motion. Hence 
we find the magnitude and position of the earth's 
elliptic orbit remain without any very sensible varia- 
tion for two or three revolutions ; but the slight 
disturbance experienced at each revolution, constantly 
accumulating in the same direction in a long series 
of years, occasions changes that cannot be lost sight 
of, and which, by a reflex influence, become in some 
instances exceedingly important in their practical 
applications. 

As it will be impossible to treat fully the complex 
subject of perturbation, I will call your attention to 
a few points about which cluster peculiar interest, in 
consequence of their great difficult}^ and the almost 
infinite reach of analysis displayed in their success- 
ful examination. 

I have already explained how it is that the disturb- 
ing influence of the sun occasions a constant fluctua- 
tion in the periodic time of the moon, accelerating it 



UNIVERSAL GRAVITATION. 143 

as the earth moves from perihelion to aphelion, and 
again retarding it from aphelion to perihelion. If, 
now, we take, a large number of revolutions of the 
moon, say a thousand, add them all up, and divide by 
one thousand, we obtain a mean period of revolution, 
which, in case the earth's orbit remains invariable, 
will never change, but will be constantly the same 
for thousands of years. By such an examination 
during the last century, the mean motion of the moon 
was obtained with great precision. Bat on a com- 
parison of eclipses recorded by the Babylonians with 
each other, it was discovered that the moon in those 
early ages required a longer time to perform her mean 
revolution than in modern times. A like comparison 
of the Babylonian eclipses with those recorded in the 
middle ages by the Arabian astronomers, confirmed 
this wonderful discovery, which was yet farther sub- 
stantiated by comparing the Arabian eclipses with 
those observed in modern times. It thus became 
manifest that, to all appearance at least, the moon's 
mean motion was growing swifter and swifter from 
century to century ; that it was approaching closer 
and still closer to the earth, and if no limit to this 
change was ever to be fixed, sooner or later the final 
catastrophe must come, and the moon be precipitated 
on the body of the earth, and the system be destroyed. 
An effort was made to account for this acceleration 
of the moon, on the theory of gravitation ; but for a 
long time there seemed to be no possibility of ren- 
dering a satisfactory explanation of the phenomena, 
far less of prescribing the limits which should cir- 
cumscribe the changes. Some, to escape from the 
difficulty, rejected entirely the ancient eclipses, and 



144 STRUCTURE OF THE UNIVERSE. 

boldly cut the knot, by pronouncing the acceleration 
as impossible, and without any foundation in fact. — 
Others admitted the fact, but finding it impossible to 
account for it on the hypothesis of gravitation, con- 
ceived the idea that the moon was moving in some 
ethereal fluid capable of resisting its motion, and pro- 
ducing a diminution in its periodic time of revolution. 
That acceleration should be the effect of resistance, may 
seem to some very strange, but a little reflection will 
render the subject clear. In case the moon's orbitual 
motion is resisted, then the centrifugal force, which 
depends on the velocity, becomes diminished, and the 
central power of the earth draws the moon closer to 
itself, decreases the magnitude of its orbit, and in 
like manner reduces the time of accomplishing one 
revolution about the earth. 

Finding no better solution of the m} r stery, and 
being obliged to acknowledge the fact that the mean 
motion of the moon was becoming swifter and swifter, 
from the action of a resisting medium, there was no 
escape from the final consequences ; and it w T as by 
some believed that the elements of decay existed, that 
the doom of the system was fixed, and although thou- 
sands, possibly millions, of years might roll away 
before the fatal day, yet it must come, slowly, but 
surely as the march of time. Such was the condition 
of the problem when Laplace gave the powers of his 
giant intellect to the resolution of this mysterious 
subject. The consequences involved gave to it an 
unspeakable interest, and the world waited with keen 
anxiety to learn the result of the investigations of this 
great geometer. Long and difficult was the struggle 
— slow and laborious the task of devising and tracing 



UNIVERSAL GRAVITATION. 145 

out the secret causes of this inscrutable phenomenon. 
The planets are weighed and poised against the 
earth, their effects computed on its orbit, the final re- 
sult of these effects determined, and the reflex influ- 
ence on the moon's motion computed with the most 
extraordinary precision. Under the searching ex- 
amination of Laplace's potent analysis, nature is 
conquered, the mystery is resolved, the law of gravi- 
tation is vindicated — the system is stable, and shall 
endure through periods whose limits God alone, and 
not man, shall prescribe. 

Follow me in a simple explanation of this most re- 
markable discovery. It has already been stated, that 
in case the earth's orbit could remain unchanged, that 
the mean period of the moon, as derived from a thou- 
sand of its revolutions, would be constant, and would 
endure without the slightest change for millions of 
years. But this permanency of the earth's orbit does 
not exist. — Laplace discovered that under the joint 
action of all the planets, the figure of the earth's 
orbit was slowly changing ; that while its longer axis 
remained invariable, that its shape was gradually be- 
coming more and more nearly circular. At the end 
of a vast period, its ellipticity would be destroyed, 
and the earth would sweep around the sun in an orbit 
precisely circular. Attaining this limit, a reversed 
action commences — the elliptic form is resumed by 
slow degrees — the eccentricity increases from age to 
age — until, at the end of millions of years, a second 
limit is reached. The motion is again reversed — :the 
orbit again opens out, approaches its circular form, 
and thus vibrates backwards and forwards in millions 
N 



146 STRUCTURE OF THE UNIVERSE. 

of years, like some mighty pendulum beating the 
slowly ebbing seconds of eternity ! 

But do you demand how this change in the figure 
of the earth's orbit can affect the moon's mean mo- 
tion ? The explanation is easy. Were it possible to 
seize the earth and hurl it to an infinite distance from 
the sun, its satellite, now released from the disturbing 
influence of this great central mass, would yield itself 
up implicitly to the earth's control. It would be 
drawn closer to its centre of motion, and its orbit 
being thus diminished, its periodic time would be 
shorter, or its motion would be accelerated or made 
swifter than it now is. This is an exaggerated hy- 
pothesis, to render more clear the effect produced by 
removing the earth farther from the sun. Now the 
change from the elliptical to the circular form, which 
has been progressing for thousands of years, in the 
earth's orbit, is, so far as it goes, carrying the earth at 
each revolution a little farther from the sun, releasing 
in this way the moon, by slow degrees, from the dis- 
turbing influence of that body ; giving to the earth a 
more exclusive control over the movements of its satel- 
lite, and thus increasing the velocity of the moon in 
its orbit from age to age. But will this acceleration 
ever reach a limit ? Never, until the earth's orbit 
becomes an exact circle, at the end of millions of 
years. Then, indeed, does the process change. At 
every succeeding revolution of the earth in its orbit, 
its ellipticity returns — its distance from the sun dimin- 
ishes — the moon is again subjected more and more to 
the action of the sun, is drawn farther and farther 
from the earth, and its periodic time slowly increases. 
Thus is acceleration changed into retardation, and at 



UNIVERSAL GRAVITATION. 147 

the end of one of these mighty cycles, consisting of 
millions of years, an exact compensation is effected, 
and the moon's motion having gone through all its 
changes, once more resumes its original value. 

I can never contemplate this wonderful revolution 
without feelings of profound admiration. Such is the 
extreme slowness of this change in the moon's mean 
motion, that in the period of three thousand years 
she has got only four of her diameters in advance of 
the position she would have occupied in case no change 
whatever had been going on. Here, then, is a cycle 
of changes extending backward to its least limit mil- 
lions of years, and extending forward to its greatest 
limit tens of millions of years, detected and measured 
by man, the existence of whose race on our globe has 
scarcely been an infinitesimal portion of the vast pe- 
riod required for the full accomplishment of this entire 
series of changes. 

May it not, then, be truly said, that man is in some 
sense immortal, even here on earth. What is time to 
him, who embraces changes in swiftly revolving worlds, 
requiring countless ages for their completion, within 
the limits of an expression so condensed that it may 
be written in a single line ? Does he not live in the 
past and in the future, as absolutely as in the present ? 
Indeed, the present is nothing — it is the past and 
future which make up existence. 

In the example of the moon's acceleration just ex- 
plained, we must not fail to notice a most remarkable 
fact. It is this: — The slow change in the figure of 
the earth's orbit, occasioned by the joint action of all 
the planets, and upon which depends the acceleration 
of the moon's mean motion, is so disguised, that but 



148 STRUCTURE OF THE UNIVERSE. 

for its reflex influence on the moon, the probability is 
it would have escaped detection for thousands of 
years. The direct effect is almost insensible, but 
being indirectly propagated to the moon, it is dis- 
played in a greatly exaggerated manner — is in this 
way detected, and finally, after incredible pains, 
traced to its origin, and demonstrates in the most 
beautiful manner the prevalence of the great law of 
universal gravitation. 

Since the general adoption of this law, the human 
mind has been, in not a few instances, disposed to 
abandon its universality, and seek for a solution of 
some intricate problem, by which it was perplexed, in 
some change or modification of the law ; but in no 
instance has the effort to fly from the law been suc- 
cessful. No matter how long and intricate the ex- 
amination, how far the mind might be carried from 
this great law, in the end it must come back and 
acknowledge its universal empire over our entire 
system. 

It has already been remarked, that one of the effects 
of the sun's disturbing influence exerted on the moon, 
was to occasion a change in the position of its 
perigee, causing it to complete an entire revolution in 
the heavens in about nine years. The theory of gravi- 
tation gave a very satisfactory account of this phe- 
nomenon generally; but when Sir Isaac Newton under- 
took the theoretic computation of the rapidity with 
which the moon's perigee should move, he found, to 
his astonishment, that no more than one half of the 
observed motion of the perigee w r as obtained from 
theory. In other language, in case the law of gravi- 
tation be true, Newton found that the moon's perigee 



UNIVERSAL GRAVITATION. 149 

ought to require eighteen years to perform its revolu- 
tion in the heavens, while observation showed that 
the revolution was actually performed in one half of 
this period. This great philosopher exhausted all his 
skill and power in the vain effort to overcome this dif- 
ficulty. He died, leaving the problem unresolved, 
bequeathing it to his successors, as a research worthy 
of their utmost efforts. 

Astronomers did not fail to recognize the high 
claims of this investigation. Gravitation was once 
more endangered. The most elaborate computations 
were made, and the results obtained by Newton were 
so invariably verified by each successive computer, 
that it seemed utterly impossible to avoid the conclu- 
sion ; — they were absolutely accurate, and that the 
theory of gravitation must be modified in its applica- 
tion to this peculiar phenomenon. At length the 
problem was taken up by the distinguished astrono- 
mer Clairaut. After repeating, in the most accurate 
manner, the extensive computations of his predeces- 
sors, reaching invariably the same results, he finally 
abandoned the law of gravitation in despair, pro- 
nounced it incapable of explaining the phenomenon, 
and undertook to frame a theory which should be in 
accordance with the facts. 

This startling declaration of Clairaut excited the 
greatest interest. An abandonment of the theory of 
gravitation was nothing less than returning once 
more to the original chaos which had reigned in the 
planetary worlds, and of commencing again the reso- 
lution of the great problem which it had long been 
hoped was entirely within the grasp of the human 
intellect. In this dilemma, when the physical astrono- 
n 2 



150 STRUCTURE OF THE UNIVERSE. 

mer had abandoned the law of gravitation in despair, 
and the legitimate defenders of the theory were mute, 
an advocate arose where one was least to be ex- 
pected. BufFon, the eminent naturalist and meta- 
physician, boldly attacked the new theory of Clairaut, 
pronounced it impossible, and defended the law of 
gravitation by a train of general reasoning, which the 
astronomer felt almost disposed to treat with ridicule. 
What should a naturalist know of such matters ? was 
rather contemptuously asked by the astronomer. It 
is true he knew bat little, yet his attack on Clairaut 
had the effect to induce the now irritated astronomer 
to return to his computations, with a view to over- 
whelm his adversary. He now determined to rest 
satisfied with nothing short of absolute perfection. — 
A certain series which had been reached by every 
computer, and the value of whose terms had been re- 
garded as decreasing by a certain law, until they 
finally became inappreciable, from their extreme mi- 
nuteness, and therefore might, without sensible error, 
be rejected, was found, on a more careful examina- 
tion, to undergo a most remarkable change in its 
character. It was true that the value of its terms did 
decrease till they became exceedingly small ; but so 
far from becoming absolutely nothing, on reaching a 
certain value, the decrease became changed into in- 
crease — the sum of the series expressing the velocity 
of the moon's perigee was in this way actually 
doubled, and Clairaut found, to his inexpressible as- 
tonishment, that the investigation which had been 
commenced with the intention of forever destroying 
the universality of the law of gravitation, resulted in 



UNIVERSAL GRAVITATION. 151 

his own defeat, and in the perfect and triumphant 
establishment of this great law. 

Thus far, in our examinations of the moon and 
earth, we have regarded their orbits as lying in the 
same plane, an hypothesis which greatly simplifies the 
complexity of their motions. This, however, is not 
the case of nature. The moon revolves in an orbit 
whose plane is inclined under an angle of about four 
degrees to the plane of the ecliptic. During half of 
its journey, it lies above the plane of the earth's 
orbit, while the remaining part of its route is per- 
formed below the ecliptic. Thus does the moon, at 
each revolution, pass through the ecliptic at two 
points, called the nodes, which points, being joined by 
a straight line, gives us the intersection of the plane 
of the moon's orbit with that of the earth. This line 
of intersection, called the line of the nodes, but for 
the disturbing influence of external causes, would re- 
main fixed in the heavens. But we know it to be 
constantly fluctuating, and in the end performing an 
entire revolution. The exact amount of this change 
has been made the subject of accurate examination, 
and the law of its movement has been found to result 
precisely from the law of gravitation. Not only is 
the line of intersection of the plane of the moon's 
orbit with that of the earth constantly changing, 
but theory, as well as observation, has ascertained 
that a series of changes are equally progressing in 
the angles of inclination of these two planes. The 
limits are narrow, but the oscillations are unceasing, 
complicating more and more the relative motions of 
these two remarkable bodies. 

In the physical examination of the revolution of 



152 STRUCTURE OF THE UNIVERSE. 

the planetary orbs by the application of the law of 
gravitation, the general features of the investigation 
are greatly simplified by the fact that the planets and 
satellites may be regarded as spherical bodies, and 
may in general be treated as though their entire mass 
were condensed into a material heavy point, situated 
at their centre. While this statement is true in its 
broader application to the theory of planetary pertur- 
bations, or even in the theory of the sun's action on 
the planets, especially the more distant ones, it is by 
no means to be admitted, when we come to a critical 
examination of the figures of the planets, and the 
influence exerted by these figures on their near 
satellites. 

In case the earth had been created an exact sphere, 
and had been projected in its orbit without any rota- 
tion on an axis, then would its globular figure have 
remained without sensible change. But as it revolves 
swiftly on its axis, the laws of motion and gravita- 
tion come in to modify the figure of the earth, and to 
change it from an exact spherical figure to one w r hich 
is flattened at the poles and protuberant at the equa- 
tor. Newton's sagacity detected this result as a 
necessary consequence of the action of gravitation, 
and he actually computed the figure of the earth from 
theory, long before any observation or measurement 
had created a suspicion that its form was other than 
spherical. The truly wonderful train of consequences 
flowing from the spheroidal form of the earth gives to 
this subject a high interest, and demands as close an 
examination of its principal features as the nature of 
our investigations will permit. 

Give to the earth, then, an exactly spherical form, 



UNIVERSAL GRAVITATION. 153 

and a diameter of 8000 miles, with a rotation on an 
axis once in twenty-four hours, and let us critically 
examine the consequences. A particle of matter 
situated on the equator is 4,000 miles from the earth's 
axis, and since it passes over the circumference of a 
circle whose radius is 4,000 miles, it will move with 
a velocity of about one thousand miles an hour. As 
we recede from the equator towards the poles, either 
north or south, the particles revolve at the extremities 
of radii constantly growing shorter and shorter, until 
finally at the exact pole there is no motion whatever. 
But in every revolving body, a centrifugal force is 
generated — a tendency or disposition to fly from the 
axis of rotation in a plane perpendicular to this axis. 

Such is the power of this centrifugal force, that if 
it were possible to make the earth rotate seventeen 
times in twenty-fours, instead of once, bodies at the 
equator would be lifted up by the centrifugal force, 
and the attraction of gravitation would be counter- 
poised, if not absolutely overcome. The force of 
gravity exerts its power in directions passing nearly 
through the centre of the earth, while the centrifugal 
force is always exerted in a direction perpendicular 
to the axis of rotation. The consequence is manifest, 
that these two forces cannot counterpoise each other, 
except in their action on particles situated on the 
equator of the revolving body. Let us consider the 
condition of a particle situated any where between 
the equator and the pole, and free to move under 
the joint action of these two forces. 

In order that such a particle may be held in equili- 
brium, the two forces must act on the same straight 
line, and in opposite directions. This is not the case 



154 STRUCTURE OF THE UNIVERSE. 

in question, for gravity draws the particle to the 
centre of the earth, while the centrifugal force urges 
it from the axis in a plane perpendicular to that axis. 
The direction of these two forces is inclined under 
an angle which is nothing at the equator, and in- 
creases from the equator to the poles. But the effect 
produced by the centrifugal force may always be ob- 
tained by the joint action of two forces, the one 
directed to the centre of the earth, the other tangent 
to the earth's surface. Substituting these two forces 
for the centrifugal force, we perceive that the partial 
force directed towards the earth's centre is destroyed 
by gravitation, while the tangential force exerts its 
full power to move the particle towards the equator 
of the earth. 

This being understood, it is manifest that as parti- 
cles are coming constantly from both poles towards 
the equator, that a change of figure in the earth must 
be effected. It becomes protuberant at the equator, 
and is flattened at the poles. 

The question now arises, whether there be any 
limit to this change of figure. In case the velocity of 
rotation continues undiminished, is there not reason 
to fear that the earth will grow more and more pro- 
tuberant at the equator, heaping up the matter higher 
and higher, till the figure of the earth be destroyed, 
and its surface rendered uninhabitable ? Theory has 
answered this important question ; and it has been 
fully demonstrated that the figure of the earth cannot 
pass a limit, which it has even now actually attained, 
and its present form will not change, from the action 
of the centrifugal force, in millions of years. A 
condition of equilibrium has been attained, and all 



UNIVERSAL GRAVITATION. 155 

further change is at an end. Indeed, if we examine 
carefully the -subject, we may readily perceive, from 
the nature of the forces, and the conditions of the 
problem, that such a result might have been antici- 
pated. As the earth grows more protuberant, chang- 
ing from the spherical form, the particles must be 
heaved up the side of this elevated ridge which belts 
the earth around the equatorial regions, and finally 
the resistance they meet from the elevation they are 
obliged to overcome, is quite equal to the moving 
force, and the two destroy each other. This point 
attained, equilibrium ensues, and further change be- 
comes impossible. 

Such is the beautiful order of nature, such the ad- 
mirable arrangement for stability and perpetuity, 
every where manifested, that the thought constantly 
comes to the mind that divine wisdom alone could 
have framed so admirable a system. 

But the question may here arise, is this a mere 
theoretic result? Has observation confirmed the 
theoretic figure? I answer that observations, the 
most numerous and diversified, have all united their 
harmonious testimony to the truth of these beautiful 
results. In executing exact measures of the degrees 
of a meridian passing through the poles round the 
earth, the length of the degree is found to increase 
from the equator towards the poles, showing that the 
curvature is more flattened as we recede from the 
equator. But a more delicate proof is found in the 
vibrations of the pendulum. A pendulum of a given 
length will vibrate with a velocity precisely propor- 
tioned to the intensity of the force of gravity which 
operates on it. But the intensity of gravity decreases 



156 STRUCTURE OF THE UNIVERSE. 

as the square of the distance from the centre increases, 
so that it is manifest that the force of gravity is less 
at the equator than at the poles, in case the surface 
at the equator is farther from the centre than at the 
poles, which is the fact asserted by theory. 

This being understood, we are prepared to deter- 
mine the exact figure of the earth, by transporting a 
pendulum of given length from the equator to differ- 
ent latitudes north and south. — The number of vibra- 
tions in one hour being accurately counted at the 
equator, as we recede north or south, will determine 
with certainty whether we are approaching to, or 
going farther from the earth's centre. These experi- 
ments have actually been performed, and with the 
most satisfactory results. The number of vibrations 
in an hour increases the farther we go north or south, 
and in a ratio giving the strongest confirmation to the 
truth of the earth's figure derived from the theoretic 
investigations — each combining to show that the 
polar diameter of the earth is but 7,893 miles, while 
the equatorial diameter is 7,924 miles, producing a 
sort of ridge or belt around the equatorial regions, 
rising about thirteen miles above the general spherical 
surface described about the polar axis as a diameter. 

More than two thousand years have passed away 
since a discovery was made, showing that the sun's 
path among the fixed stars was slowly changing. — 
The point at which it crossed the equatorial line, and 
which for ages had been regarded as fixed, was finally 
detected to have a slow retrograde motion, producing 
the precession of the equinoxes. The fact was received, 
but, no depth of penetration, no stretch of intellectual 
vigor could divine the cause of this inexplicable 



UNIVERSAL GRAVITATION. 157 

change. Another fact was revealed about the same 
time. It was found by attentive examination, that 
the north pole of the heavens, the point in which the 
prolongation of the earth's axis pierces the celestial 
sphere, was actually changing, by slow degrees, its 
place among the fixed stars. The bright star which, 
in former ages, had marked the place of the pole, and 
whose circle of diurnal revolution was scarcely to be 
perceived from its smallness, as centuries slowly 
glided by, was increasing its distance from the pole, 
gradually describing around it a circle of greater 
radius. An attentive examination of the stars near 
the pole soon demonstrated the fact, that it was an 
actual motion of the pole, and not of the stars in its 
neighborhood. 

Now, incredible as this statement may appear, 
modern science has traced these phenomena, the revo- 
lution of the equinoctial point, and the movement of 
the north pole of the heavens, to a common origin, 
and has demonstrated, in the clearest manner, that 
they are both consequences of the spheroidal figure 
of the earth, which we have just examined. It is not 
my design to enter into an elaborate investigation of 
this wonderful subject, but, in accordance with the 
plan already announced, I cannot leave you with a 
mere announcement of a truth so startling, without 
some effort to explain how this may be. The subject 
is difficult, but favored by your close attention, I do 
not despair of rendering it approximately intelligible. 

Let us conceive the earth's axis to be a solid bar 
of iron driven through the centre of the earth, com- 
ing out at the poles, and extending indefinitely to- 
wards the sphere of the fixed stars. Now turn this 
O 



158 STRUCTURE OF THE UNIVERSE. 

axis up until it stands perpendicular to the plane of 
the orbit in which the earth revolves around the sun. 
Then do the equator and ecliptic exactly coincide, and 
if the fixed stars are at a distance nearly infinite, the 
point in which the earth's axis prolonged pierces the 
heavens will appear stationary, so far as the revolu- 
tion of the earth in its orbit is concerned. Now if 
this iron axle could be grasped by some giant hand, 
and drawn away from its upright or perpendicular 
position, the solid earth would turn with it, and the 
equator, ceasing to coincide with the ecliptic or plane 
of the earth's orbit, comes to be inclined to it, under 
an angle precisely equal to the angle through which 
the axis has been inclined. It is thus seen that no 
change can be wrought on the position of the axis, 
that does not involve a corresponding change in the 
whole earth, and especially in the plane of the equa- 
tor, which must ever remain perpendicular to the axis 
in all its positions. 

The reverse of this proposition is equally manifest. 
If the solid earth be seized at the equator, and be turned 
up or down, the axis will participate in this movement, 
and its change will exhibit itself in the changed posi- 
tion of the point in which it meets the celestial sphere. 
One step more, and the difficulty is surmounted. — 
Conceive a flat wheel of wood floating on still water. 
Through its centre pass an axle which stands perpen- 
dicular to the surface of the wheel and water. So 
long as the wheel floats level, the axle stands erect, 
but in case the north half of the wheel is tilted down 
under the water, the south half at the same time rising 
out of the water, the axis will tilt towards the north. 
Bring the wheel again to its level position. Now 



UNIVERSAL GRAVITATION. 159 

plunge the eastern portion of the wheel below the 
surface. — The axis now is tilted towards the east. — 
The experiment is simple, and shows that, in case 
the successive portions of the wheel be submerged, 
the axis will always be tilted towards the point which 
goes under first. To reverse the experiment: in case 
we take hold of the axle and turn it east, it sinks the 
eastern half of the wheel below the surface of the 
water, while the western half is raised out of it, and 
then in case we make the upper extremity of the 
axis follow round the circumference of a circle whose 
surface is parallel to that of the water, and whose 
centre is exactly above the centre of the wheel, it 
will be seen that, as the axle moves round, successive 
portions of the wheel are submerged, until finally the 
water line will have divided the wheel into all its 
successive halves, and will have successively coincided 
with every possible diameter of the wheel. 

Now for the application. The level surface of the 
water is the level plane of the earth's orbit, the 
wheel is the earth's equator, and the axle is the 
earth's axis of rotation. One-half of the equator is 
constantly submerged below the plane of the ecliptic 
— the other half rises above it. But the water line, 
or the intersection of these two planes, the equinoc- 
tial line, cannot remain fixed in the same line. A 
power does seize the equator and plunge successive 
halves of it beneath the plane of the ecliptic, chang- 
ing perpetually the water line, until finally each half 
in succession, into which all its diameters can be di- 
vided, are sunk below the surface, or plane of the 
ecliptic, thus causing the earth's axis to tilt over to- 
wards the portions successively submerged, until it 



160 STRUCTURE OF THE UNIVERSE. 

finally sweeps entirely round and comes to resume 
its first position. 

But do you now demand what power seizes the 
earth's protuberant equator, and tilts it successively 
towards every point of the compass? I answer, that 
the power is lodged in the sun and moon, and it is 
their combined action which works out these wonder- 
ful results. In case the sun and moon were so situated 
as always to be in the plane of the earth's equator, 
then they would have no power to change the position 
of the equator. But we know that they are not in 
this plane, except when passing through it, and are 
found sometimes on the north and sometimes on the 
south side of it. Wherever either of them may be, 
the nearest half of the redundant matter about the 
earth's equator will be more forcibly attracted than 
the remote half, and the equator will be tilted towords 
the attracting body, and the axis of the earth will fol- 
low the movement of the equator to which it is firmly 
fixed. 

Thus does the earth's whole solid mass sway to the 
motion of the ring of matter heaped up around the 
equator, delicately and beautifully sensitive to all the 
changes in the relative places of the sun and moon. 
Neither the earth nor its axis are ever, for one mo- 
ment, released from the action of these remote bodies. 
However slight the effects, however varied in action, 
oscillating to every point within certain prescribed 
limits, the stability is preserved, and the final effect is 
a small retrograde motion of the equinox at the end 
of every year, and a slight change in the place of the 
pole of the heavens. 

But there is no isolated matter in the universe. — 



UNIVERSAL GRAVITATION. 161 

Every particle of matter attracts every other particle 
of matter, and it is impossible for the sun and moon 
to exert any influence on the equatorial ring of mat- 
ter which belongs to our globe, without feeling, in 
their turn, the reaction of this ring on themselves. — 
The remote and ponderous sun may, in consequence 
of its vast size and distance, escape from any effect 
capable of being detected by observation. But this is 
not the case with the moon. Her proximity to the 
earth and diminutive mass, render her peculiarly 
sensitive to the influence of the redundant matter at 
the earth's equator, and as her attraction tilts the 
plane of the earth's equator, so does the equatorial 
ring tilt the plane of the moon's orbit. These effects 
have been accurately observed and measured, and 
strange to relate, their exact values have exhibited 
the figure which belongs to the earth with far greater 
precision than can be obtained from measures on its 
surface. We may even go farther, for such is the in- 
timate relationship between the earth and its attend- 
ant satellite, that there is scarcely a question can be 
asked with reference to the one, that is not answered 
by the other. 

If we demand the weight of the earth when com- 
pared with the sun, the moon answers. If the excess 
of the equatorial diameter of the earth over the polar 
be required, the moon answers. If the homogenity of 
the interior of the solid earth be required, the moon 
replies. If the thickness of the earth's crust is sought 
for, question the moon, and the answer comes. If 
you would know the sun's distance from the earth, 
ask the moon. If the permanency of the axis of rota- 
tion be required, ask the moon, and she alone yields 
o2 



162 STRUCTURE OF THE UNIVERSE. 

a satisfactory reply. Finally, if curiosity leads us to 
inquire whether the length of the day and night, the 
revolution of the earth on its axis, be uniform, or 
whether it may not have changed by a single second 
in a thousand years, we go to the moon for an an- 
swer, and in each and every instance her replies to 
all these profound and mysterious questions are clear 
and satisfactoiy. How wonderful the structure of the 
universe ! How gigantic the power of the human 
intellect ! If all the stars of heaven were struck 
from existence ; if every planet and satellite which 
the eye and the telescope descry, inside and beyond 
the earth's orbit, were swept away forever, and the 
sun, earth and moon alone remained for the study of 
man, and as evidences of the being and wisdom of 
God, in the exquisite adjustments of this system, in the 
reciprocal influences of its three bodies, in their vast 
cycles of configuration, in their relative masses, mag- 
nitudes, distances, motions, and perturbations, there 
would remain themes sufficient for the exercise of the 
most exalted genius, and proof of the being of God, 
so clear and positive, that no sane mind could com- 
prehend it and disbelieve. 



LECTURE VI. 

THE STABILITY OF THE PLANETARY SYSTEM. 

When, by the application of a single great law, the 
mind had succeeded in resolving the difficult problems 
presented by the motions of the earth and its satel- 
lite, the moon, it rose to the examination of the higher 
and more complicated questions of the stability of 
the entire system of planets, satellites, and comets, 
which are found to pursue their courses round the 
sun. The number of bodies involved in this investi- 
gation, their magnitudes and vast periods of revolu- 
tion, their great distances from the observer, and the 
exceeding delicacy of the required observations, com- 
bined with the high interest which attaches itself to 
the final result, have united to render this investiga- 
tion the most wonderful which has ever employed the 
energies of the human mind. 

To comprehend the dignity and importance of this 
great subject, let us rapidly survey the system, and 
moving outward to its known boundaries, mark the 
number and variety of worlds involved in the- investi- 
gation. Beginning, then, at the great centre, the 
grand controlling orb, the sun, we find its magnitude 
such as greatly to exceed the combined masses of all 
its attendant planets. Indeed, if these could all be 
arranged in a straight line on the same side of the 
sun, so that their joint effect might be exerted on that 
body, the centre of gravity of the entire system thus 

(163) 



164 STRUCTURE OF THE UNIVERSE. 

located, would scarcely fall beyond the limits of the 
sun's surface. At a mean distance of 36,000,000 of 
miles from the sun we meet the nearest planet, Mer- 
cury, revolving in an orbit of considerable eccentricity, 
and completing its circuit around the sun in a period 
of about eighty-eight of our days. This world has 
a diameter of only 3,140 miles, and is the smallest 
of the old planets. Pursuing our journey, at a dis- 
tance of 68,000,000 of miles from the sun, we cross 
the orbit of the planet Venus. Her magnitude is 
nearly equal to that of the earth. Her diameter is 
7,700 miles, and the length of her year is nearly 225 
of our days. The next planet we meet is the earth, 
whose mean distance from the sun is 95,000,000 of 
miles. The peculiarities which mark its movements, 
and those of its satellite, have been already discussed. 
Leaving the earth, and continuing our journey out- 
ward, we cross the orbit of Mars, at a mean distance 
from the sun of 112,000,000 of miles. This planet is 
4,100 miles in diameter, and performs its revolution 
around the sun in about 687 days, in an orbit but 
little inclined to the plane of the ecliptic. Its features, 
as we shall see hereafter, are more nearly like those 
of the earth than any other planet. Beyond the 
orbit of Mars, and at a mean distance from the sun 
of about 250,000,000 of miles, we encounter a group 
of small planets, eight in number, presenting an 
anomaly in the system, and entirely different from 
anything elsewhere to be found. These little planets 
are called asteroids. Their orbits are, in general, 
more eccentric, and more inclined to the ecliptic, than 
those of the other planets ; but the most remarkable 
fact is this : — that their orbits are so nearly equal in 



STABILITY OF THE PLANETARY SYSTEM. 165 

size, that when projected on a common plane, they 
are not enclosed, the one witnin the other, but actually 
cross each other. 

We shall return to an examination of these won- 
derful objects hereafter. At a mean distance of 
485,000,000 of miles from the sun, we cross the orbit 
of Jupiter, the largest and most magnificent of all the 
planets. His diameter is nearly 90,000 miles. He is 
attended by four moons, and performs his revolution 
round the sun in a period of nearly twelve years. — 
Leaving this vast world, and continuing our journey 
to a distance of 890,000,000 of miles from the sun, 
we cross the orbit of Saturn, the most wonderful of 
all the planets. His diameter is 76,068 miles, and he 
sweeps round the sun in a period of nearly twenty-nine 
and a half years. He is surrounded by several broad 
concentric rings, and is accompanied by no fewer than 
seven satellites or moons. The interplanetary spaces 
we perceive are rapidly increasing. The orbit of 
Uranus is crossed at a mean distance from the sun of 
1,800,000,000 of miles. His diameter is 35,000 miles, 
and his period of revolution amounts to rather more 
than eighty-four of our years. He is attended by six 
moons, and pursues his journey at a slower rate than 
any of the interior planets. Leaving this planet, we 
reach the known boundary of the planetary system, 
at a distance of about 3,000,000,000 of miles from 
the sun. Here revolves the last discovered planet, 
Neptune, attended by one, probably by two moons, 
and completing his vast circuit about the sun in a 
period of one hundred and sixty-four of our years. — 
His diameter is eight times greater than the earth's, 
and he contains an amount of matter sufficient to 



166 STRUCTURE OF THE UNIVERSE. 

form one hundred and twenty-five worlds such as 
ours. 

Here we reach the known limit of the planetary- 
worlds, and standing at this remote point and looking 
back towards the sun, the keenest vision of man could 
not descry more than one solitary planet along the line 
we have traversed. The distance is so great, that 
even Saturn and Jupiter are utterly invisible, and the 
sun himself has shrunk to be scarcely greater than a 
fixed star. 

There are certain great characteristics which dis- 
tinguish this entire scheme of worlds. They are all 
nearly globular — they all revolve on axes — their orbits 
are all nearly circular — they all revolve in the same 
direction around the sun — the planes of their orbits 
are but slightly inclined to each other, and their moons 
follow the same general laws. With a knowledge of 
these general facts, it is proposed to trace the recip- 
rocal influences of all these revolving worlds, and to 
learn, if it be possible, whether this vast scheme has 
been so constructed as to endure while time shall 
last, or whether the elements of its final dissolution 
are not contained within itself, either causing the 
planets, one by one, to drop into the sun, or to recede 
from this great centre, released from its influence, to 
pursue their lawless orbits through unknown regions 
of space. 

Before proceeding to the investigation of the great 
problem of the stability of the universe, let as examine 
how far the law of gravitation extends its influence 
over the bodies which are united in the solar system. 
A broad and distinct line must be drawn between 
those phenomena, for which gravitation must render 



STABILITY OF THE PLANETARY SYSTEM. 167 

a satisfactory account, and those other phenomena, 
for which it is in no wise responsible. In the solar 
system we find, for example, that all the planets re- 
volve in the same direction around the sun, in orbits 
slightly elliptical, and in planes but little inclined to 
each other. Neither of these three peculiarities is in 
any way traceable to the law of gravitation. 

Start a planet in its career, and, no matter what be 
the eccentricity of its orbit, the direction of its move- 
ment, or the inclination of the plane in which it pur- 
sues its journey, once projected, it falls under the 
empire of gravitation, and ever after, this law is ac- 
countable for all its movements. We are not, there- 
fore, to regard the remarkable constitution of the 
solar system as a result of any of the known laws of 
nature. 

If the sun were created, and the planetary worlds 
formed and placed at the disposal of a being possessed 
of less than infinite wisdom, and he were required so 
to locate them in space, and to project them in orbits, 
such that their revolutions should be eternal, even 
with the assistance of the known laws of motion and 
gravitation, this finite being would fail to construct 
his required system. 

Let it be remembered, that each and every one of 
these bodies exerts an influence upon all the others. 
There is no isolated object in the system. Planet 
sways planet, and satellite bends the orbit of satellite, 
until the primitive curves described, lose the simplicity 
of their character, and perturbations arise, which may 
end in absolute destruction. There is no chance 
work in the construction of our mighty system. Every 
planet has been weighed and poised, and placed pre- 



168 STRUCTURE OF THE UNIVERSE. 

cisely where it should be. If it were possible to drag 
Jupiter from its orbit, and cause him to change places 
with the planet Venus, this interchange of orbits 
would be fatal to the stability of the entire system. 
In contemplating the delicacy and complexity of the 
adjustment of the planetary worlds, the mind cannot 
fail to recognize the fact that, in all this intricate 
balancing, there is a higher object to be gained than 
the mere perpetuity of the system. 

If stability had been the sole object, it might have 
been gained by a far simpler arrangement. If God 
had so constituted matter that the sun might have 
attracted the planets, while these should exert no in- 
fluence over each other — that the planets might have 
attracted their satellites, while these were free from 
their reciprocal influences — then, indeed, a system 
would have been formed, whose movements would 
have been eternal, and whose stability would have 
been independent of the relative positions of the 
worlds, and the character of their orbits. Give to 
them but space enough in which to perform their rev- 
olutions around the sun, so that no collisions might 
occur, freed from this only danger, every planet, and 
every satellite, will pursue the same undeviating 
track throughout the ceaseless ages of eternity. 

If this statement be true, it may be demanded, why 
such a system was not adopted. It is impossible for 
us to assign all the reasons which led to the adoption 
of the present complicated system. Of one thing, 
however, we are certain : — If God designed that in 
the heavens his glory and his wisdom should be de- 
clared, and that in the study of his mighty works, his 
intelligent creatures should rise higher and higher to- 



STABILITY OF THE PLANETARY SYSTEM. 169 

wards his eternal throne, then, indeed, has the present 
system been admirably constituted for the accomplish- 
ment of this grand design. To have acquired a 
knowledge of a system constituted of independent 
planets, free from all mutual perturbations, would 
have required scarcely no effort to the mind, when 
compared with that put forth in the investigation of 
the present complex construction of the planetary 
system. The mind would have lost the opportunity 
of achieving its greatest triumphs, while the evidence 
of infinite wisdom displayed in the arrangement and 
counterpoising of the present system would have been 
lost forever. There is one other thought which here 
suggests itself with so much force that I cannot turn 
away from it. We speak of gravitation as some in- 
herent quality or property of matter, as though mat- 
ter could not exist in case it were deprived of this 
quality. This is, however, a false idea. Matter might 
have existed independent of any quality which should 
cause distant globes to influence each other. — 
This force called gravitation, even admitting that it 
must have an existence, no special law of its action 
could have forced itself on matter to the exclusion of 
all other laws. Why does this force diminish as the 
square of the distance at which it operates, increases? 
There are almost an infinite number of laws, accord- 
ing to which an attraction might have exerted itself, 
but there is no one which would have rendered the 
planets fit abodes for sentient beings, such as now 
dwell on them, and which would at the same time 
have guaranteed the perpetuity of the system. Ad- 
mitting, then, that matter cannot be matter, without 
exerting some influence on all other matter, (which 
P 



170 STRUCTURE OF THE UNIVERSE. 

I am unwilling to admit), in the selection of the law 
of the inverse square of the distance, there is the 
strongest evidence of design. 

If we rise above the law of gravitation to the Great 
Author of nature, and regard the laws of motion and 
of gravitation as nothing more than the uniform ex- 
pressions of his will, we perceive at once the impos- 
sibility of constructing the universe in such manner 
that the sun should attract the planets, without these 
attracting each other ; or that the planets should at- 
tract their satellites without, in turn, being recipro- 
cally influenced by their satellites ; for this would be 
equivalent to saying that the will of the same Al- 
mighty Being should exert itself, and not exert itself, 
at the same moment, which is impossible. As there 
is but one God, so there is but one kind of matter, 
governed by one law, applied by infinite wisdom to 
the formation of suns and systems without number, 
crowding the illimitable regions of space, all moving 
harmoniously, fulfilling their high destiny, and all sus- 
tained by the single arm of divine Omnipotence. 

We now proceed to an examination of the great 
question, Is the system of worlds by which we are 
surrounded, and of which our earth and its moon form 
a part, so constructed that, under the operation of the 
known laws of nature, it shall forever endure, without 
ever passing certain narrow limits of change, which 
do not in any way involve its stability ? 

It is well known that the planets revolve in ellip- 
tical orbits of small eccentricity — that under the action 
of the primitive impulse by which they were projected 
in their orbits, they would have moved off in a straight 
line, with a velocity proportioned to the intensity of 



STABILITY OF THE PLANETARY SYSTEM. 171 

the impulse, and which would have endured forever ; 
but being seized by the central attraction of the sun, 
at the moment of starting in their career, the joint 
action of these two forces, bends the planet from its 
straight direction, and cause it to commence a curvi- 
linear path, which carries it round the sun. 

The question which first presents itself is this : — If 
the central force lodged in the sun has the power to 
cause a planet to diverge from the straight line in 
which, but for this, it would have moved — if it draw 
it into a curved path, will not this central force, which 
is ever active, finally overcome, entirely, the impul- 
sive force originally given to the planet, draw it closer 
and closer to the sun in each successive revolution, in 
a spiral orbit, until, finally, the planet shall fall into 
the sun, and be destroyed forever? This question 
arises independent of the extraneous influence which 
the planets exert over each other. It refers to a soli- 
tary globe revolving around the sun, under the influ- 
ence of a central force which varies its action as does 
the law of gravitation. The problem has been sub- 
mitted to the most rigorous mathematical examina- 
tion, and a result has been obtained which settles 
the question in the most absolute manner. The 
amount by which the central force, in a moment of 
time, overcomes the effect produced by the primitive 
impulse, is a quantity infinitely small, and of the second 
order. If it were found to be infinitely small in each 
moment of time, then might it accumulate so that, at 
the end of a vast period, it might become finite and 
appreciable. But because it is of the second order of 
infinitely small quantities, before it can become an infi- 
nitely small quantity of the first order, a period equal 



172 STRUCTURE OF THE UNIVERSE. 

to infinite ages must roll by, and to make a finite ap- 
preciable quantity out of this, an infinite cycle of 
years must roll round an infinite number of times ! 

Such is the answer given by analysis to this wonder- 
ful question. " Is there no change ? " demands the 
astronomer. " Yes," answers the all-seeing analysis. 
" When will it become appreciable ? " asks the astron- 
omer. "At the end of a period infinitely long, repeated 
an infinite number of times," is the reply. 

Having settled this important question, it remains 
now to examine whether the mutual attractions of 
the planets on each other may not, in the end, change 
permanently the form of their orbits, and lead, ulti- 
mately, to the destruction of the system. To com- 
prehend more readily the nature of the examination, 
let us review the points involved in the permanency 
of our orbit. 

Take, for example, our own planet, the earth. It 
now revolves in an elliptic orbit, whose magnitude is 
determined by the length of its longer axis, and by 
its eccentricity. These elements are readily deduced 
from observation. If it were possible to construct 
this orbit of some material, like wire, which would 
permit us to take it up and locate it in space at will, 
to enable us to give it the position now occupied by 
the actual orbit of the earth, we must first carry 
its focus to the sun's centre ; we must then turn its 
longer axis around this centre as a fixed point, until 
the nearest vertex of the wire orbit shall fall upon 
that point of the earth's orbit which is at this time 
nearest to the sun. Having accomplished this, the 
axes will coincide in their entire length, and to make 
the orbits coincident, we must revolve the artificial 



STABILITY OF THE PLANETARY SYSTEM. 173 

one around the now common axis, until its plane shall 
fall upon the actual orbit of the earth. 

If, now, change should ever come, in the absolute 
coincidence of these two orbits, regarding the iron one 
as fixed and permanent, the orbit of nature may vary 
from it in any one or all of the following ways : — 
First. The natural orbit, all other things remaining 
the same, may leave the fixed orbit by a variation of 
eccentricity ; — that is, it may become more or less 
nearly circular. Second. The planes of the orbits re- 
maining coincident, the curves may separate from 
each other, in consequence of an angular movement 
of the longer axis of the natural orbit, by means of 
which the vertex of the natural curve shall be carried 
to the right or to the left of the vertex of the fixed 
one. Third. While these causes are operating to pro- 
duce change, an increase of deviation may be occa- 
sioned by the fact that the two planes may become 
inclined to each other, thus causing the natural orbit 
to lie partly above and partly below the fixed one. — 
These, then, are the several ways in which the orbits 
of the planets may change ; and to settle the question 
of stability, we must ascertain whether these changes 
actually exist, and whether any of them, in case they 
do exist, and are progressing constantly in the same 
direction, will ever prove fatal to the permanency of 
the system, finally accomplishing its absolute destruc- 
tion, or rendering it unfit for the sustentation of that 
life which now exists upon the planet. 

By a close examination of this great subject, both 
theoretically and practically, it is found that the sys- 
tem is so constituted, that not a single planet or satel- 
lite revolves in an orbit absolutely invariable. Theory 
p 2 



174 STRUCTURE OF THE UNIVERSE. 

demonstrates that such changes must exist, and ob- 
servation confirms this great truth, by showing that 
they actually do exist. 

Draw, in imagination, a straight line from the sun's 
centre, through the perihelion, or nearest point to the 
sun of the earth's orbit, and let it be extended to the 
outermost limits of the entire system. On this locate 
the perihelion points of the orbits of all the planets, 
and in these points fix the planets themselves. They 
are now all on the same side of the sun, the longer 
axes of their orbits are in the same direction, and 
they are all located at their nearest distance from the 
sun, or in perihelion. The planes of the orbits are 
inclined to each other under their proper angles, and 
they all intersect in a common line of nodes passing 
through the sun's centre. Now give the entire group 
of planets their primitive impulse, and at the same 
instant they start in their respective orbits round the 
sun. Now, in case no perturbations existed, the peri- 
helion points, the inclinations, and the lines of nodes, 
would remain fixed forever, and although millions of 
years might pass away before the planets would again 
resume their primitive position with reference to each 
other, yet the time would come when a final restora- 
tion would be effected. 

At the end of 164 years, Neptune will have com- 
pleted its revolution round the sun, and will return to 
its starting point. All the other planets will have 
performed several revolutions, but each, on reaching 
the point of departure, will find the perihelion of its 
orbit changed in position, the inclination altered, and 
the line of nodes shifted. These changes continue 
until the longer axes of the orbits, which once coin- 



STABILITY OF THE PLANETARY SYSTEM. 175 

cided, radiate- from the sun in all directions. The 
lines of nodes, once common, now diverge under all 
angles, the inclinations increasing or decreasing, and 
even the figures of the orbits undergoing constant 
mutation ; and the grand question arises, whether 
these changes, no matter how slow, are ever to con- 
tinue progressing in the same direction, until all the 
original features of the system shall be effaced, and 
the possibility of return to the primitive condition 
destroyed forever. 

Such a problem would seem to be far too deep and 
complicated ever to be grasped by the human intel- 
lect. It is true that no single mind was able to ac- 
complish its complete solution, but the advance made 
by one has been steadily increased by another, until, 
finally, not a question remains unanswered. The so- 
lution is complete, yielding results of the most won- 
derful character. 

We shall examine this great problem in detail, and 
commence with the figure of the orbit of any planet, 
our earth, for example. 

The amount of heat received from the sun by the 
earth depends, other things being the same, on the 
minor axis of its ecliptic orbit. Any change in the 
eccentricity operates directly to increase or decrease 
the shorter axis, and consequently to increase or de 
crease the mean annual amount of heat received 
from the sun. Now we know that animal and vege- 
table life is adjusted in such way that it requires al- 
most exact uniformity in the mean annual amount of 
heat which it shall enjoy. An increase or decrease 
of two or three degrees in temperature would make 
an entire revolution in the animals and plants belong- 



176 STRUCTURE OF THE UNIVERSE. 

ing to the region experiencing such a change. If, 
then, it be true that the eccentricity of the earth's 
orbit is actually changing, under the combined action 
of the other planets, may this change continue so far 
as to subvert the order of nature on its surface ? — 
This question has been answered in the most satis- 
factory manner. 

It is found that the greater axes of the planetary 
orbits are subjected to slight and temporary varia- 
tions, returning, in comparatively short periods, to 
their primitive values. This important fact guaran- 
tees the permanency of the periodic times, so that it 
becomes possible to deduce, with the utmost precision, 
the periodic times of the planets, from the mean of a 
large number of revolutions. That of the earth is 
now so accurately known, and so absolutely invaria- 
ble, that we know what it will be a million of years 
hence, should the system remain as it now is, as per- 
fectly as at the present moment. But neither of these 
elements secures the stability of the eccentricity, or 
of the minor axis. Lagrange, however, demonstrated 
a relation between the masses of the planets, their 
major axes and eccentricities, such, that while the 
masses remain constant, and the axes invariable, the 
eccentricity can only vary its value through extremely 
narrow limits. These limits have been assigned, be- 
yond which the change can never pass, and within 
these narrow bounds we find the orbits of all the 
planets slowly vibrating backward and forward, in 
periods which actually stun the imagination. 

This remarkable law for the preservation of the 
system would not hold in any other organization. It 
demands orbits nearly circular, with planes nearly co- 



STABILITY OF THE PLANETARY SYSTEM. 177 

incident, with, periodic times related as are those of 
the planets, and the planets themselves located as 
they actually are. No interchange of orbits is admis- 
sible ; but, constituted as the system now is, the per- 
petuity is absolutely certain, so far as the change of 
eccentricity is concerned. 

Let us now examine the changes which affect the 
position of the major axis in its own plane. The 
perihelion of every orbit is found to be slowly advanc- 
ing. Nor is this advance ever to be changed into a 
retrograde motion. The movement is ever progres- 
sive in the same direction, and the perihelion points of 
all the orbits are slowly sweeping round the sun. — 
That of the earth's orbit accomplishes its revolution 
in one hundred and eleven thousand years ! How won- 
derful the fact, that such discoveries should be made 
by man, whose entire life is but a minute fraction of 
these vast periods of time ! 

Owing to a retrograde motion in the vernal equi- 
nox, carrying it around in the opposite direction in 
25,868 years, the perihelion and equinox pass each 
other once in 20,984 years. Knowing their relative 
positions at this moment, and their rates of motion, 
it is easy to compute the time of their coincidence. 
Their last coincidence took place 4,089 years before 
the Christian era, or about the epoch usually assigned 
for the creation of man. The effect of the coinci- 
dence of the perihelion with the vernal equinox, is to 
cause an exact equality in the length of spring and 
summer, compared with autumn and winter. In other 
language, the sun will occupy exactly half a year in 
passing from the vernal to the autumnal equinox, and 



178 STRUCTURE OF THE UNIVERSE. 

the other half in moving from the autumnal to the 
vernal equinox. 

At present, the line of equinoxes divides the earth's 
elliptic orbit into two unequal portions. The smaller 
part is passed over in the fall and winter, causing the 
earth to be nearer the sun at this season than in sum- 
mer, and making a difference in the length of the two 
principal seasons, summer and winter, of some seven- 
teen and a half days. This inequality, which is now 
in favor of summer, will eventually be destroyed, and 
the time will come when the earth will be farthest 
from the sun during the winter, and nearest in the 
summer. But at the end of a great cycle of more 
than 20,000 years, all the changes will have been 
gone through, and, in this respect, a complete com- 
pensation and restoration will have been effected. 

This epoch of subordinate restoration will find the 
perihelion of the earth's orbit located in space far 
distant from the point primitively occupied. Five of 
these grand revolutions of 20,984 years must roll 
round before the slow movement of the perihelion 
shall bring it back to its starting point. 110,000 
years will then restore the axis of the earth's orbit, 
and the equinoctial line, nearly to their relative po- 
sitions to each other, and to the same region of abso- 
lute space occupied at the beginning of this grand 
cycle. 

If, now, we direct our attention to the other planets, 
we find their perihelion points all slowly advancing 
in the same direction. That of the orbit of Jupiter 
performs its revolution round the sun in 186,207 
years, while the perihelion of Mercury's orbit occu- 
pies more than 200,000 years in completing its circuit 



ST ABILITY OF THE PLANETARY SYSTEM. 1/9 

round the sun. To effect a complete restoration of 
the planetary orbits to their original position, with 
reference to their perihelion points, will require a 
grand compound cycle, amounting to millions of 
years. Yet the time will come when all the orbits 
will come again to their primitive positions, to start 
once more on their ceaseless journeys. 

In the changes of the eccentricities, it will be re- 
membered, the stability of the system was involved. 
Should these changes be ever progressive, no matter 
how slowly, a time would finally come when the 
original figure of the orbit would be destroyed, the 
planet either falling into the sun, or sweeping away 
into unknown regions of space. But a limit is as- 
signed, beyond which the change can never pass. — 
Some of the planetary orbits are becoming more cir- 
cular, others growing more elliptical ; but all have their 
limits fixed. The earth's orbit, for example, should 
the present rate of decrease of eccentricity continue, 
in about half a million of years will become an exact 
circle. There the progressive motion of the changes 
stops,and it slowly commences to recover its ellipti city. 
This is not the case with the motions of the perihelia. 
Their positions are in no way involved in the well 
being of a planet, or in its capacity to sustain the 
life which exists on its surface ; and since the stability 
of the system is not endangered by progressive 
change, it ever continues in the same direction, until 
the final restoration is effected, by an entire revolu- 
tion about the sun. 

Let us now examine the inclinations of the plane- 
tary orbits. Here it is found that there is no guaran- 
tee for the stability of the system, provided the angles 



180 STRUCTURE OF THE UNIVERSE. 

under which the orbits of the planets are inclined to 
each other do not remain nearly the same forever. — 
If changes are found to exist, by which the inclina- 
tions are made to increase, without stopping and re- 
turning to their primitive condition, then is the perpe- 
tuity of the system rendered impossible. Its fair 
proportions must slowly wear away, the harmony 
which now prevails be destroyed, and chaos must 
come again. 

Commencing again with the earth, we find that, 
from the earliest ages, the inclination of the earth's 
equator to the ecliptic has been decreasing. Since 
the measure of Eratosthenes, 2,078 years ago, the de- 
crease has amounted to about 23' 44", or about half a 
second every year. Should the decrease continue, in 
about 85,000 years the equator and ecliptic would co- 
incide, and the order of nature would be entirely 
changed ; — perpetual spring would reign throughout 
the year, and the seasons would be lost forever. Of 
this, however, there is no danger. The diminution 
will reach its limit in a comparatively short time, 
when the decrease of inclination will change into 
an increase, and thus slowly rocking backwards and 
forwards in thousands of years, the seasons shall ever 
preserve their appointed places, and seed time and 
harvest shall never fail. These changes of inclina- 
tion are principally due to the perturbations of Venus, 
and arising from configurations, will be ultimately 
entirely compensated. 

The angles under which the planetary orbits are 
inclined to each other are in a constant state of mu- 
tation. The orbit of Jupiter at this time forms an 
angle with the ecliptic of 4,731 seconds, and thi3 



STABILITY OF THE PLANETARY SYSTEM. 181 

angle is decreasing at such a rate that, in about 20,000 
years the planes would actually coincide. This would 
not affect the well being of the planets or the sta- 
bility of the system, but should the same change now 
continue, the angle between the orbits might finally 
come to fix them even at right angles to each other, 
and a subversion of the present system would result. 

A profound investigation of the problem of the 
planetary inclinations, accomplished by Lagrange, re- 
sulted in the demonstration of a relation between the 
masses of the planets, the principal axes of their 
orbits, and the inclinations, such that, although the 
angles of inclination may vary, the limits are narrow, 
and they are all found slowly to oscillate about their 
mean positions, never passing the prescribed limits, 
and securing, in this particular, the perpetuity of the 
system. 

Here, again, we are presented with the remarkable 
fact, that whenever mutation involves stability, this 
mutation is of a compensatory character, always re- 
turning upon itself, and, in the long run, correcting 
its own effects. If all this mighty system was organ- 
ized by chance, how happens it that the angular 
motions of the perihelia of the planetary orbits are 
ever progressive, while the angular motions of the 
planes of the orbits are vibrating ? Design, positive 
and conspicuous, is written all over the system, in 
characters from which there is no escape. 

We now proceed to an examination of the lines in 
which the planes of the planetary orbits cut each 
other, or the lines in which they intersect a fixed 
plane. These are called the lines of nodes. They all 
pass through the sun's centre, and, in case they ever 

Q 



182 STRUCTURE OF THE UNIVERSE. 

were coincident, they now radiate from a common 
point in all directions. 

Here is an element in no degree involving in its 
value the stability of the system, and from analogy 
we already begin to anticipate that its changes, what- 
ever they may be, will probably progress always in 
the same direction. This is actually the case. The 
nodes of the planetary orbits are all slowly retrograd- 
ing on a fixed plane, and in vast periods, amounting 
to thousands of years, accomplish revolutions, which, 
in the end, return them to their primitive positions. 

Thus are we led to the following results. Of the 
two elements which fix the magnitude of the plane- 
tary orbits, the principal axes, and the eccentricity, the 
axes remain invariable, while the eccentricity oscil- 
lates between narrow and fixed limits. In the long 
run, therefore, the magnitudes of the orbits are 
preserved. 

Of the three elements which give position to the 
planetary orbits, viz : the place of the perihelion, the 
lines of nodes, and the inclinations, the two first ever 
vary in the same direction, and accomplish their res- 
toration at the end of vast periods of revolution, 
while the inclinations vibrate between narrow and 
prescribed limits. 

One more point, and we close this wonderful inves- 
tigation. The last question which presents itself is 
this : — May not the periodic times of the planets be 
so adjusted to each, as that the results of certain con- 
figurations may be ever repeated without any com- 
pensation, and thus, by perpetual accumulation, finally 
effect a destruction of the system ? 

If the periodic times of two neighboring planets 



STABILITY OF THE PLANETARY SYSTEM. 183 

were exact multiples of the same quantity, or if the 
one was double the other, or in any exact ratio, then 
the contingency would arise, above alluded to, and 
there would be perturbations which would remain 
uncompensated. A near approach to this condition 
of things actually exists in the system, and gave 
great trouble to geometers. It was found, on com- 
paring observations, that the mean periods of Jupiter 
and Saturn were not constant — that one was on the 
decrease, while the other was on the increase. This 
discovery seemed to disprove the great demonstration 
which had fixed as invariable the major axes of 
the planetary orbits, and guaranteed the stability of 
the mean motions. It was not until after Laplace 
had instituted a long and laborious research, that the 
phenomenon was traced to its true origin, and was 
found to arise from the near commensurability of the 
periodic times of Jupiter and Saturn — five of Jupiter's 
periods being nearly equal to two of Saturn's. In 
case the equality were exact, it is plain that if the 
two planets set out from the same straight line drawn 
from the sun, at the end of a cycle of five of Jupiter's 
periods, or two of Saturn's, they would be again found 
in the same relative positions, and whatever effect the 
one planet had exerted over the other would again be 
repeated under the same precise circumstances. Hence 
would arise derangements which would progress in 
the same direction, and eventually lead to permanent 
derangement of the system. 

But it happens that five of Jupiter's periods are not 
exactly equal to two of Saturn's, and in this want of 
equality safety is found. The difference is such, 
that the point of conjunction of the planets does not 



184 STRUCTURE OF THE UNIVERSE. 

fall at the same points of their orbits, but at the end 
of each cycle is in advance by a few degrees. Thus 
the conjunction slowly works round the orbits of the 
planets, and, in the end, the effect produced on one 
side of the orbit is compensated for on the other, and a 
mean period of revolution comes out for both planets, 
which is invariable. In the case of Jupiter and Sat- 
urn, the entire compensation is not effected until after 
a period of nearly a thousand years. 

A similar inequality is found to exist between the 
earth and Venus, with a period much shorter, and 
producing results much less easily observed. In no 
instance do we find the periods of any two planets 
in an exact ratio. They are all incommensurable 
with each other, and in this peculiar arrangement 
we find the stability of the entire system is secured. 

So far, then, as the organization of the great plan 
etar} r system is concerned, we do not find within 
itself the elements of its own destruction. Mutation 
and change are everywhere found — all is in motion — 
orbits expanding or contracting — their planes rocking 
up and down — their perihelia and nodes sweeping in 
opposite directions round the sun, — but the limits of 
all these changes are fixed ; — these limits can never 
be passed, and at the end of a vast period, amounting 
to many millions of years, the entire range of fluctua- 
tion will have been accomplished, the entire system, 
planets, orbits, inclinations, eccentricities, perihelia, 
and nodes, will have regained their original values 
and places, and the great bell of eternity will have 
then sounded one. 

Having reached the grand conclusion of the sta- 
bility of the system of planets, in their reciprocal in- 



STABILITY OF THE PLANETARY SYSTEM. 185 

fluences, and that no element of destruction is found 
in the organization, we propose next to inquire 
whether the same features are stamped on the sub- 
ordinate groups composing the planetary system. — 
As our limits will not permit us to enter into a full 
examination of all the subordinate groups, we shall 
confine our remarks to our own earth and its satellite, 
Jupiter and his satellites, and to Saturn, his rings and 
moons. We shall, in this examination, find it practi- 
cable to answer, to some extent, the inquiry as to 
whether either of these systems has received any 
shock from external causes. We know nothing as 
to the future, and can, in this particular, only form 
our conjectures as to what is to be, from what has 
been. 

We commence our inquiry by an examination of 
two questions, viz : — Is the velocity of rotation of the 
earth on its axis absolutely invariable ? Has the re- 
lation between the earth and moon ever been dis- 
turbed by any external cause ? There is nothing so 
important to the well being of our planet and its in- 
habitants as absolute invariability in the period of its 
axical rotation. The sidereal day is the great unit 
of measure for time, and is of the highest consequence 
in all astronomical investigations. If causes are 
operating, either to increase or decrease the velocity 
of rotation, a time will come when the earth will 
cease to rotate, or else acquire so great a velocity as 
to destroy its figure, and, in the end, scatter its parti- 
cles in space. 

It is difficult to ascertain from theory a perfectly 
satisfactory answer to the question of the invariable 
velocity of rotation of the earth, but Laplace has 
a 2 



186 STRUCTURE OF THE UNIVERSE. * 

demonstrated that the length of the day has not va- 
ried by the hundredth of one second during the last 
two thousand years — that is, the length of the day is 
neither greater nor less than it was two thousand 
years ago by the hundredth of a second. The reason- 
ing leading to this remarkable result is simple, and 
may be readily comprehended by all. Two thousand 
years ago, the duration of the moon's period of revo- 
lution around the earth was accurately determined, 
and was expressed in days and parts of a day. The 
measure of the same period has been accomplished 
in our own time, and is expressed in days and parts 
of a day. Now all the causes operating to change 
the moon's period of revolution are known, and may 
be applied. When this is done, it is found that the 
moon's period now and two thousand years ago, agree 
precisely, being accomplished in the same number of 
days and parts of a day — which would be impossible, 
if the unit of measure, the day, had varied ever so 
slightly. 

The extraordinary relation existing between the 
moon's period in her orbit and the time occupied in 
her axical rotation, gives us the opportunity of ascer- 
taining whether our system has received any external 
shock. These two periods are so accurately adjusted, 
that in all respects an exact equality exists. The 
moon ever turns the same hemisphere to the earth, 
and ever will, unless some external cause should 
arise to disturb the perfect harmony which now reigns. 
It is not my purpose to explain why it is that this 
phenomenon exists. I merely desire to state, that 
this delicate balancing of periods furnishes an admi- 
rable evidence that, for several thousands of years, at 



STABILITY OF THE PLANETARY SYSTEM. 187 

least, no shock has been received by the earth and its 
satellite. Steadily have they moved in their orbits, 
subject only to the influence of causes originating in 
the constitution of the mighty system of which they 
constitute a part. 

Moving out to a more complex system, we find in 
the remarkable arrangement of the satellites of Jupi- 
ter, a delicate test for the action of sudden and extra- 
neous causes. Here we find the periodic times of the 
satellites so related, that a thousand periods of the 
first, added to two thousand periods of the third, will 
be precisely equal to three thousand periods of the 
second. This delicate balancing of periods would be 
destroyed by the action of any external shock, such 
as might be experienced from the collision of a comet 
sweeping through the system. Thus far, we know 
that no disturbance has entered, and a knowledge of 
facts will now pass down to posterity, which will give 
the means of ascertaining exactly the influence of 
all disturbing causes which do not form a part of the 
great system. 

The last subordinate group, and the most extraor- 
dinary one to which I will at this time direct your 
attention, is that of Saturn and his rings. Here we 
find a delicacy of adjustment and equilibrium far ex- 
ceeding any thing yet exhibited in our examinations. 
This great planet is surrounded certainly by two, 
probably by three, immense rings, which are formed 
of solid matter, in all respects like that constituting 
the central body. These wonderful appendages are 
nowhere else to be found, throughout the entire solar 
system, at least with certainty. Their existence has 
elsewhere been suspected, but around Saturn they are 



188 STRUCTURE OF THE UNIVERSE. 

seen with a perfection and distinctness which defies 
all scepticism as to their actual existence. The di- 
ameter of the outer ring is no less than 176,000 miles. 
Its breadth is 21,000 miles, while its thickness does not 
exceed one hundred miles. The inner ring is separa- 
ted from the outer one by a space of about 1,800 miles, 
— its breadth 34,000 miles, its inner edge being about 
20,000 miles from the surface of the planet. — Its thick- 
ness is the same as that of the outer ring. These ex- 
traordinary objects are rotating in the same direction 
as the planet, and with a velocity so great that objects 
on the exterior edge of the outer ring are carried 
through space with the amazing velocity of nearly 
50,000 miles an hour, or nearly fifty times more 
swiftly than the objects on the earth's equator. 

What power of adjustment, can secure the stability 
of these stupendous rings ? No solid bond fastens 
them to the planet — isolated in space, they hold their 
places, and revolving with incredible velocity around 
an imaginary axis, they accompany their planet in 
its mighty orbit round the sun. Such is the exceed- 
ing delicacy with which this system is adjusted, that, 
the slightest external cause once deranging the equili- 
brium, no readjustment would be effected. The rings' 
would be thrown on the body of the planet, and the 
system would be destroyed. 

To understand the extraordinary character of this 
system, we will explain a little more fully the three 
different kinds of equilibrium. The first is called an 
equilibrium of instability, and is exemplified in the 
effort to balance a rod on the tip of the finger. The 
slightest deviation from the exact vertical, increases 
itself constantly, until the equilibrium is destroyed. — 



STABILITY OF THE PLANETARY SYSTEM. 189 

In case the same rod be balanced on its centre on the 
finger, it presents an example of an equilibrium of 
indifference ; that is, if it be swayed slightly to the one 
side or the other, there is no tendency to restore itself, 
or to increase its deviation. — It remains indifferent to 
any change. Take the same rod, and suspend it like 
a pendulum. Now cause it to deviate from the ver- 
tical to the right or left, and it returns of itself to the 
condition of equilibrium. This is an equilibrium of 
stability. We have already seen that this is the kind 
of equilibrium which exists in the planetary system. 
There are constant deviations, but a perpetual effort 
is making to restore the object to its primitive 
condition. 

Now in case the rings of Saturn are homogeneous, 
equally thick, and exactly concentric with the planet, 
their equilibrium is one of instability. The smallest 
derangement would find no restorative power, and 
would even perpetuate and increase itself, until the 
system is destroyed. For a long time it was believed 
that the rings were equally thick, and concentric with 
the planet, but when it was discovered that such fea- 
tures would produce an equilibrium of instability, and 
that there existed no guarantee for the permanency 
of this exquisite system, an analytic examination was 
made, which led to this singular result, viz : — To 
change the equilibrium of instability into one of sta- 
bility, all that is necessary is to make the ring thicker 
or denser in some parts than in others, and to cause 
its centre of position to be without the centre of the 
planet, and to perform around that centre a revolution 
in a minute orbit. Finding these conditions analyti- 
cally, it now became a matter of deep interest to as- 



190 STRUCTURE OF THE UNIVERSE. 

certain whether these conditions actually existed in 
nature. The occasional disappearance of the ring, in 
consequence of its edge being presented to the eye of 
the observer, gave a capital opportunity of determin- 
ing whether it was of uniform thickness. On these 
rare occasions, in the most powerful telescopes, the 
ring remains visible edgewise, and looks like a slen- 
der fibre of silver light drawn across the diameter of 
the planet. In the gradual wasting away of the two 
extremities of the ring, it has been remarked, that the 
one remains visible longer than the other. As the ring 
is swiftly revolving, neither extremity can, in any 
sense, be regarded as fixed, and hence sometimes the 
one, sometimes the other, fades first from the sight. 
An exactly uniform thickness in the ring would ren- 
der such a phenomenon impossible, and hence we 
conclude, that the first condition of stability is ful- 
filled, — the rings are not equally thick throughout. 

The micrometer was now applied to detect an ec- 
centricity in the central point of the ring. Recent 
examinations by Struve and Bessel have settled thi3 
question in the most satisfactory manner. The centre 
of the ring does not coincide with that of the planet, 
and it is actually performing a revolution around the 
centre of the planet in a minute orbit, thus forming 
the second delicate condition of equilibrium. The 
analogy of the great system is unbroken in the sub- 
ordinate one. For more than two hundred years 
have these wonderful circles of light whirled in their 
rapid career under the eye of man, and freed from 
all external action, they are so poised that millions 
of years shall in nowise affect their beautiful organi- 
zation. Their graceful figures and beautiful light 



STABILITY OF THE PLANETARY SYSTEM. 191 

shall greet the eyes of the student of the heavens 
when ten thousand years shall have rolled away. 

Thus do we find that God has built the heavens in 
wisdom, to declare his glory, and to show forth his 
handy- work. There are no iron tracks, with bars and 
bolts, to hold the planets in their orbits. Freely in 
space they move, ever changing, but never changed ; 
poised and balancing; swaying and swayed ; disturb- 
ing and disturbed, onward they fly, fulfilling with un- 
erring certainty their mighty cycles. The entire 
system forms one grand complicated piece of celestial 
machinery ; — circle within circle ; wheel within wheel ; 
cycle within cycle ; — revolutions so swift as to be 
completed in a few hours ; movements so slow that 
their mighty periods are only counted by millions of 
years. Are we to believe that the Divine Architect 
constructed this admirably adjusted system to wear 
out, and to fall in ruins, even before one single revolu- 
tion of its complex scheme of wheels had been per- 
formed? No. — I see the mighty orbits of the planets 
slowly rocking to and fro, their figures expanding and 
contracting, their axes revolving in their vast periods; 
but stability is there. Every change shall wear 
away, and after sweeping through the grand cycle of 
cycles, the whole system shall return to its primitive 
condition of perfection and beauty. 



LECTURE VII. 

THE DISCOVERY OF NEW PLANETS. 

In the earliest ages of the world, the keen vision 
of the old astronomers had detected the princi- 
pal members of the planetary system. Even Mer- 
cury, which habitually hovers near the sun, and whose 
light is almost constantly lost in the superior bril- 
liancy of that luminary, did not escape the eagle 
glance of the primitive students of the stars. For 
many thousand years no suspicion arose in the mind, 
as to the existence of other planets, belonging to the 
great scheme, and which had remained invisible from 
their immense distance or their minute dimensions. — 
Indeed the grand investigations which have recently 
engaged our attention, the mutation of the planetary 
orbits, their perpetual oscillations and final restora- 
tion, the equilibrium of the whole system, had been 
prosecuted and completed before the mind gave itself 
seriously to the contemplation of invisible worlds. 

The singularly inquisitive genius of Kepler, over 
whom analogy seems to have ever played the tyrant, 
in an examination of the interplanetary spaces, find- 
ing these to increase with regularity in proceeding 
outward from the sun, until reaching the space be- 
tween Mars and Jupiter, which was out of all pro- 
portion too great, conceived the idea that an invisible 
planet revolved in this space, and thus completed the 

R (193, 



194 STRUCTURE OF THE UNIVERSE. 

harmony of the system. The space from the orbit of 
Mercury to that of Venus is 31,000,000 of miles ; from 
the orbit of Venus to that of the earth is 27,000,000 of 
miles ; from the earth's orbit to that of Mars is 50,- 
000,000 of miles, but between the orbit of Mars and 
that of Jupiter, there exists the enormous interval of 
359,000,000 of miles. The order is again resumed 
between the orbits of Jupiter and Saturn, and from 
these slender data Kepler boldly predicted that a time 
would come when a planet would be found interme- 
diate between the orbits of Mars and Jupiter, whose 
discovery would establish a regular progression in 
the interplanetary spaces. For nearly two hundred 
years this daring speculation was regarded as one of 
the wild dreams of a great, but visionary mind. 

Towards the close of the eighteenth century, when 
the planetary orbs had been studied with great care, 
and a comparatively accurate knowledge of their per- 
turbations had been reached, certain unexplained ir- 
regularities gave rise to the suspicion that the move- 
ments of Saturn might be disturbed by the action of 
an unknown planet revolving in a vast orbit, remote 
from, and far beyond that of Saturn. These specula- 
tions led to no serious results, and it was only by a 
fortunate accident that, on the 13th of March, 1781, 
Sir William Herschel noticed a small star of remarka- 
ble appearance, which happened to fall in the field 
of his telescope. On applying a greater magnifying 
power, the strange star showed unequivocal symptoms 
of increased dimensions. Its position among the 
neighboring stars was noticed with care, and by an 
examination on the following evening, the stranger 
was found to have sensibly changed position. A few 



DISCOVERY OF NEW PLANETS. 195 

nights sufficed to establish the fact that the newly dis- 
covered body was actually a wandering star, and not 
for a moment dreaming of the discovery of a new 
planet, Herschel announced to the world that he had 
found a remarkable comet. Efforts were made to ob- 
tain the orbit of the stranger, on the hypothesis, that 
like those of all the then known comets, it was ex- 
tremely elongated. Maskelyn and Lexell soon reached 
the conclusion that no eccentric orbit could possibly 
represent the motions of the newly discovered star, 
and on a close and diligent examination, it was at 
last discovered to be a primary planet, revolving in 
an orbit nearly circular, and almost coincident with 
the plane of the ecliptic. Its motion was progressive, 
like the other planets, and its vast orbit was only 
completed at the end of eighty-four of our years. Its 
distance from the sun was found to be no less than 
1,800,000,000 of miles, and its dimensions such that out 
of it might be formed more than eighty worlds as 
large as the earth. 

This great discovery excited the highest interest in 
the astronomical world. From the earliest ages, the 
mighty orbit of Saturn had been regarded as forming 
the boundary of the vast scheme of planets depend- 
ant on the sun. Its slow and majestic motion, its 
great period and distance, and the wonderful mag- 
nificence of its rings and moons, seemed to render it 
a fitting object to guard the frontiers of the mighty 
system with which it was associated. But the su- 
premacy of Saturn was now gone forever, and its 
sentinel position was usurped by Uranus, whose 
grand orbit expanded to twice their original dimen- 
sions the boundaries of the solar system. Far sweep- 



196 STRUCTURE OF THE UNIVERSE. 

ing in the depths of space, this new world pursued 
its solemn journey, flinging back the light of its 
parent orb, steadily obedient to the great law of 
universal gravitation, which held the old planets true 
to their changing orbits. 

Another unit in the number of interplanetary spaces 
was thus given, and the law which might possibly 
regulate the distances of the planets from the sun 
was sought after with an interest and perseverance 
which could not long fail of its reward. No exact 
progression was indeed discovered, but the following 
remarkable empirical law was detected by Prof. Bode : 
Write the series 3 6 12 24 48 96 192, &c. 
Add to each term 444 4 444 4 
The sums are 4 7 10 16 28 52 100 196. 

Now if 10 be assumed as the earth's distance from 
the sun, the other terms of the series will represent 
very nearly the distances of the planets, thus : 

4 7 10 16 28 52 100 196 

Mercury, Venus, Earth, Mars, — , Jup., Saturn, Uranus. 
The fifth term in the series is blank, and falls exactly 
in the enormous interval which exists between the 
orbits of Mars and Jupiter, precisely where Kepler 
had predicted a new planet would be found. As early 
as 1784, three years after the discovery of Uranus, 
Baron de Zach, struck with the remarkable law of 
Bode, even went so far as to compute the probable 
distance and period of the now generally suspected 
planet. The impression that a new world would 
soon be added to the system grew deeper and stronger 
in the minds of astronomers, until finally, in 1800, at 
a meeting held at Lilienthal, by six distinguished ob- 
servers, the subject was discussed with deep earnest- 



DISCOVERY OF NEW PLANETS. 197 

ncss, and it was finally resolved that the long sus- 
pected, but yet undiscovered world, should be made 
the object of strict and persevering research. The 
range of the Zodiac was divided into twenty-four 
parts, and distributed among an equal number of ob- 
servers, whose duty it was to scrutinize their particu- 
lar regions, and detect, if possible, any moving body 
which might show itself among the fixed stars. 

Tn case it were possible to note down, with perfect 
precision, the relative places and magnitudes of all 
the stars in a given region, any subsequent changes 
which might occur would be easily recognized. In 
other language, could a daguerreotype picture of any 
region in the heavens be made to-night, and at the 
end of a year another picture of the same region 
could be taken, by comparing the number of stars in 
the one picture with that in the second, in case any 
one had wandered away from its place, or a stranger 
had come to occupy a place within the limits of the 
pictured region, it would be an easy matter to ascer- 
tain either the lost star, or the newly arrived stranger. 
Now, although a daguerreotype picture cannot be 
had, yet, by observation, the exact relative positions 
of all the visible stars may be mapped out, and a 
picture formed, which shall become the ready means 
of detecting future changes. 

Such was the method of examination adopted by 
the congress of astronomers assembled at Lilienthal, 
in 1800. The organization was made. — Baron de 
Zach was elected president, and Schroeter was chosen 
perpetual secretary. To those who have paid but 
little attention to the circumstances under which this 
strange enterprise was undertaken, nothing can ap- 
r 2 



198 STRUCTURE OF THE UNIVERSE. 

pear more wild and chimerical. To commence a 
prolonged research for an invisible world, one that 
no keenness of vision could detect, and which never 
could be revealed but by telescopic aid, a world whose 
magnitude was so small that it would not appear so 
large as a star of the smallest size visible to the naked 
eye, and one which must be sought out and detected, 
not by its planetary disc, but by its wanderings 
among thousands of stars, which it in all respects 
resembled, and from which it could in no wise be dis- 
tinguished, but by its motion, seemed like a wasting 
of time and utter throwing away of labor and energy. 
Piazzi, of Palermo, in Sicily, was one of the planet 
searching association. He had already distinguished 
himself as an eminent and accurate observer, and had 
with indefatigable zeal constructed a most extensive 
catalogue of the relative places of the fixed stars, 
and thus, in some sense, anticipated a part of the la- 
bor that the research for the suspected planet contem- 
plated. Assisted by his own and by preceding cata- 
logues, he entered on the great work with the energy 
and zeal which distinguished all his great astronomi- 
cal efforts. On the evening of the first day of the 
year 1801, this astronomer had his attention attracted 
by a small star in the constellation of the Bull, which 
he took to be one recorded in the catalogue of Mayer ; 
but on examination, it was found not to occupy any 
place either on Mayer's or his own catalogue. Yet it 
was so small that it was an easy matter to account 
for this fact, by its having been overlooked in preced- 
ing explorations of the region in which it was found. 
With intense anxiety the astronomer awaited the 
evening of the following night, to settle the great 



DISCOVERY OF NEW PLANETS. 199 

question whether the newly detected star was a 
fixed or moving body. On the evening of the 2d of 
January he repaired to his observatory, and so soon 
as the fading twilight permitted, directed the telescope 
to the exact point in which, on the preceding evening, 
his suspicious star had been located. The spot was 
blank ! But another, which was distant 4' in right 
ascension, and 3i' in declination, which, on the pre- 
vious night had certainly been vacant, was now 
gleaming with the bright little object which, on the 
preceding evening, had so earnestly fixed his atten- 
tion, and for which he was again so anxiously seek- 
ing. Night after night he watched its retrograde mo- 
tion, — a motion precisely such as it ought to have, in 
case it were the long desired planet, — until, on the 
12th, it became stationary, and then slowly commenced 
progressing in the order of the signs. Piazzi was 
unfortunately taken ill ; his observations were sus- 
pended, and such was the difficulty of intercommuni- 
cation, that, although he sent intelligence of his dis- 
covery to Bode and Orani, associates in the great 
enterprise, the newly discovered body was already 
lost in the rays of the sun, before it became possible 
to renew the train of observations by which its orbit 
might be made known. Piazzi feared to announce 
the newly discovered body to be the suspected planet. 
His observations were few, and he was the only per- 
son in the world who had seen it. Bode no sooner 
received the intelligence of its discovery, than he at 
once pronounced it to be the long sought planet, and 
from the scanty materials furnished by Piazzi, Olbers, 
Burkhart, and Gauss, all computed the elements of its 
orbit, settled the great fact that it was a superior 



200 STRUCTURE OF THE UNIVERSE. 

planet, and that its orbit was included between those 
of Mars and Jupiter. Some doubt, however, yet 
rested on the subject, and the disengagement of the 
planet from the beams of the sun was awaited with 
the deepest interest. 

Several months passed away. Every eye and every 
telescope was directed to the region in the heavens 
where the new planet was expected to be found. The 
most scrutinizing search was made for its rediscovery, 
but without any success. But for the high reputation 
of Piazzi, his well known accuracy and honesty, 
doubts would have arisen as to whether he had not 
been self-deceived, or was intentionally deceiving 
others. The subject became of deeper and deeper in- 
terest. The world began to sneer at a science which 
could find a body in the heavens, and then forever lose 
it. We must remember that Piazzi had followed it 
through only about 4° out of 360° of its orbit, and 
on this narrow basis a research was to be instituted, 
having for its object the determination of the exact 
position which the lost planet must occupy. Gauss, 
then comparatively a young man, and little known as 
a computer, had conceived a new method of deter- 
mining the orbits of comets, from a very few and very 
closely consecutive observations. Here was an ad- 
mirable opportunity of giving a practical proof of 
the power of his new method. The long and intri- 
cate calculation was finished, the place of the lost 
planet determined, the telescope was directed to the 
spot, and lo ! the beautiful little orb flashed once more 
on the eager gaze of the youthful astronomer. For 
one entire year had the planet been sought in vain, 
and but for the powerful analysis of Gauss, nothing 



DISCOVERY OF NEW PLANETS. 201 

but years of persevering toil could have wiped away 
the reproach which rested on astronomy. 

A sufficient number of observations were soon 
made to reveal the orbitual elements of the planet, 
now named Ceres. It was found, in all respects, to 
harmonize in its movements with the older planets, 
and its orbit filled precisely the blank in the strange 
empirical law discovered by Bode. The period and 
distance hypothetically computed from that law six- 
teen years before, by Baron de Zach, were verified in 
the most remarkable manner by the actual period and 
distance of Ceres. Order and beauty now reigned in 
the planetary system, and a most signal victory had 
crowned the efforts of astronomical science. 

The only remarkable difference between the new 
planet and the old ones, consisted in its minute size, 
the great obliquity of its orbit, and the dense atmos- 
phere by which it appears to be surrounded. Its di- 
ameter is so small as to render its measure next to 
impossible, and the best practical astronomers differ 
widely in their results. Sir William Herschel makes 
its diameter only 163 miles, while Schroeter cannot 
make it less than ten times that quantity. The mean 
of these two extremes is probably near the truth. — ■ 
No satellites have been found in attendance on this 
minute planet, although Sir William Herschel sus- 
pected the existence of two at one time, a suspicion 
which subsequent observations have not confirmed. 

The beautiful order established in the solar system 
by the discovery of CerCs was a subject of the highest 
gratification to the whole astronomical world, and 
especially to those who had been instrumental in 
reaching this remarkable result. An opportunity had 



202 STRUCTURE OF THE UNIVERSE. 

scarcely presented itself for the expression of delight 
occasioned by this announcement, before all interested 
were startled by a declaration from Dr. Olbers, of 
Bremen, that he had found another planet on the 
evening of the 28th of March, 1802, with a mean 
distance and periodic time almost identical with those 
of Ceres. This discovery broke through all the analo 
gies of the solar system, and presented the wonder- 
ful anomaly of two planets revolving in such close 
proximity, that their orbits, projected on the plane of 
the ecliptic, actually intersected each other. 

The new planet was called Pallas, and is of a mag- 
nitude about equal to that of Ceres. Its orbit is 
greatly inclined to the plane of the ecliptic, and its 
eccentricity is very considerable. The existence of 
these small planets, in such near proximity, for a long 
while perplexed astronomers. At length Olbers sug- 
gested that these minute bodies might be the frag- 
ments of a great world, rent asunder by some internal 
convulsion of sufficient power to produce the terrific 
result, but of a nature entirely beyond the boundary 
of conjecture. 

Extraordinary as this hypothesis may appear, the 
results to which it led are not less remarkable. If a 
world of large size had been actually burst into frag- 
ments, it is easy to perceive that these fragments, all 
darting away in the orbits due to their impulsive forces, 
would start from the same point, and hence would 
return at different intervals indeed, but would all 
again pass through the point of space occupied by 
the parent orb when the convulsion occurred. Hav- 
ing found two of these fragmentary worlds, the point 
of intersection of their orbits would indicate the re- 



DISCOVERY OF NEW PLANETS. 203 

gion through which the other fragments might be 
expected to pass, and in which they might possibly 
be discovered. So reasonable did the views of Olbers 
appear, that his suggestions were immediately acted 
upon by himself and several distinguished observers, 
and on the 2d of September, 1804, Mr. Harding, of 
Lilienthal, while scrutinizing the very region indicated 
by Olbers, detected a star of the eighth magnitude, 
which seemed to be a stranger, and was soon recog- 
nized to be another small planet, fully agreeing, in 
all its essential characteristics, with the theory of 
Olbers. The new world was named Juno, and is re- 
markable for the eccentricity of its orbit. Its diame- 
ter has not been well determined, owing to its minute 
size. This discovery gave to the theory of Olbers the 
air of reality, and finding the nodes of the three frag- 
ments to lie in the opposite constellations Cetus and 
Virgo, he prosecuted his researches in these regions 
with redoubled energy and zeal. 

His efforts were not long without their reward. On 
the 29th of March, 1807, he detected the fourth of his 
fragments in the constellation Virgo, and very near 
the point through which he had, for four years, been 
waiting to see it pass. This was a most wonderful 
discovery, and almost fixed the stamp of truth upon 
the most extraordinary theory which had ever been 
promulgated. This new asteroid was named Vesta, 
and for nearly forty years, the examinations which 
were conducted revealed no new fragment, and it be- 
gan to be regarded as positively ascertained, that all 
the small bodies revolving in this region had been re- 
vealed to the eye. 

But on the 8th day of Dec, 1845, Mr. Hencke, of 



204 STRUCTURE OF THE UNIVERSE. 

Dreisen announced to the world the discovery of an- 
other asteroid, which was named Astrea. Before two 
years had rolled round, the same indefatigable ob- 
server discovered a sixth member in this wonderful 
group, which was called Hebe. His success induced 
other observers to undertake a similar examination, 
and in a very short time the researches of Mr. Hind, 
of London, were rewarded by the discovery of a 
seventh and eighth asteroid, which were named Iris 
and Flora. 

Thus have we no less than eight of these minute 
worlds, revolving in orbits so nearly equal, that for 
weeks and months these miniature orbs may sweep 
along in space, almost within hail of each other. Let 
us now return to an examination of the hypothesis 
of Olbers, that these are the fragments of a world of 
large size, which once occupied an orbit intermediate 
between those of Mars and Jupiter. 

If any internal convulsion could burst a world and 
separate its fragments, it is readily seen that the frag- 
ments of largest mass would move in orbits more 
nearly coincident with that of the original planet, 
while the smaller fragments would revolve in orbits 
greatly inclined to the primitive one. This condition 
is wonderfully fulfilled among the asteroids. The 
larger planets, Ceres and Vesta, revolve in orbits 
with small inclinations to the ecliptic, while the 
smaller objects are in some instances found to move 
in planes with very great inclinations. The force 
necessary to burst a planet, and to give to its frag- 
ments certain orbits, has been computed by Lagrange, 
and he finds that in case any fragment is projected 
with an initial velocity one hundred and twenty-one 



DISCOVERY OF NEW PLANETS. 205 

times greater than that of a cannon ball, it would 
become a direct comet, with a parabolic orbit, while a 
primitive velocity one hundred and fifty-six times 
greater than that of a cannon ball would cause the 
fragments to revolve with a retrograde motion in the 
curve of a parabola. Any less powerful force would 
cause the fragment to revolve in ellipses ; and it is 
probable that the force which operated to produce the 
asteroids was not more than twenty or thirty times 
greater than that of a cannon ball. Although the 
theory of Olbers has received new accessions of 
strength from the discovery of every new asteroid, it 
would be wrong to regard it as one of the demon- 
strated truths of astronomy. In the mean time, pow- 
erful efforts are making to scour the heavens, and a 
method of observation has been proffered to the Acad- 
emy of sciences, of Paris, by which all the visible 
fragments may be discovered within a period of four 
years. Should this plan, which contemplates a di- 
vision of the heavens among different astronomers, be 
adopted, volunteers have already presented them- 
selves, and the most interesting results may be 
anticipated. 

From this curious branch of astronomical inquiry 
we turn to one of still deeper interest. In the exam- 
inations for new planets, thus far, the telescope has 
been the sole instrument of research. Conjectures 
based upon analogical reasoning, it is true, guided 
the instrumental examinations, but the mind had 
never dared to rise to the effort of reasoning its way 
analytically to the exact position of an unknown 
body. It has been reserved for our own day to pro- 
duce the most remarkable and the boldest theorizing 





2 



























206 STRUCTURE OF THE UNIVERSE. 

which has ever marked the career of astronomical 
science. — I refer to the analytic effort to trace out the 
orbit, define the distance, and weigh the mass of an 
unknown planet as far beyond the extremest known 
planet as it is from the sun. 

I am fully aware of the difficulties by which I am 
surrounded, when I invite your attention to this com- 
plex and intricate subject ; and I know how utterly 
impossible it is, in a popular effort, to do any kind of 
justice to the intricate and involved reasoning of the 
great geometers, who have not only rendered them- 
selves, but the age in which we live, illustrious by 
their efforts to resolve this, the grandest problem 
which has ever been presented for human genius. — 
Trusting to your close attention, I shall attempt to 
exhibit some faint outline of the train of reasoning 
and the kind of research employed in rescuing an un- 
known world from the viewless regions of space in 
which it has been tracing its unknown orbit for ages 
commensurate with the existence of the great system 
of orbs of which it constitutes a part. 

After the discovery of the planet Uranus, by Sir 
William Herschel, geometers were not long in fitting 
it with an orbit which represented in the outset, with 
accuracy, its early movements. With this orbit it 
became possible to trace its career backwards, and 
to define its position among the fixed stars for fifty 
or one hundred years previous to the date of its dis- 
covery. This was actually done, with the hope of 
finding that the place of the planet had been observed 
and recorded by some astronomer, who ranked it 
among the fixed stars. This hope was not disap- 
pointed. The planet, believed to be a fixed star, had 



DISCOVERY OF NEW PLANETS. 207 

been seen and observed no less than nineteen differ- 
ent times, by four different observers, through a period 
running back nearly one hundred years previous to 
the discovery of its planetary character by Herschel. 
These remote observations were of the greatest value 
as data for the determination of the elements of its 
elliptic orbit, and for the computation of the mean 
places, which might serve to predict its position in 
coming years. 

A distinguished astronomer, M. Bouvard, of the 
Paris Academy of Sciences, about thirty years ago, 
undertook the analytic investigation of the movements 
of Uranus, and a computation of exact tables. He 
was met, however, by difficulties which, in the state 
of knowledge as it then existed, with reference to 
this planet, were absolutely insurmountable. He 
found it quite impossible to obtain any orbit which 
would pass through the places of the planet deter- 
mined after its discovery, and through those positions 
which had been fixed previous to that epoch. In this 
dilemma it became necessary to reject the old obser- 
vations as less reliable than the new ones, and the 
learned computer leaves the problem for posterity to 
resolve, carefully abstaining from any absolute de- 
cision in the case. 

His orbit, based upon the new or modern observa- 
tions, and his tables being computed, it was hoped 
that the theoretic places of the planet would there- 
after coincide with the observed places, and that all 
discrepancies which might not be fairly chargeable to 
errors of observation, would be removed. In this ex- 
pectation, however, the astronomical world was dis- 
appointed ; and while the tables of Bouvard failed 



208 STRUCTURE OF THE UNIVERSE. 

absolutely to represent the ancient observations, in a 
few years they were but little more truthful in giving 
the positions actually filled by the planet under the 
telescope. The discrepancies between the theoretic 
and actual places of the planet began to attract at- 
tention many years since. As early as 1838, Mr. 
Airy, Astronomer Royal of England, on a compari- 
son of his own observations with the tables, found 
that the planet was out of its computed track, by a 
distance as great as the moon's distance from the 
earth, and that it was actually describing an orbit 
greater than that pointed out by theory. It seemed 
that this remote body was breaking away from the 
sun's control, or that it was operated on by some un- 
known body deep sunk in space, and which thus far 
had escaped the scrutinizing gaze of man. 

These deviations became so palpable as to attract 
general attention, and various conjectures were made 
with reference to their probable cause. Some were 
disposed to regard the law of gravitation as some- 
what relaxed in its rigorous application to this remote 
body ; others thought the deviation attributable to 
the action of some large comet, which might sway 
the planet from its course; while a third set of philos- 
ophers conjectured the existence of a large satellite 
revolving about Uranus, and from whose attraction 
the planet was caused to swerve from the computed 
orbit. These conjectures were not sustained by any 
show of reasoning, and were of no scientific value. 

Such was the condition of the problem when it was 
undertaken by a young French astronomer, not quite 
unknown to fame in his own country, but compara- 
tively at the beginning of his scientific career. The 



DISCOVERY OF NEW PLANETS. 209 

friend of Arago, Leverrier's Cometary Investigations, 
and more especially his researches of the motions of 
Mercury, had gained for him the confidence of this 
distinguished savant, and Arago urged on his young 
associate the importance of the great problem pre- 
sented in the perturbations of Uranus, and induced 
him to abandon other investigations, and concentrate 
all the energies of his genius on this profound and 
complex investigation. 

The extraordinary powers of Leverrier as a mathe- 
matical astronomer had been so successful^ displayed 
in his researches of the motions of Mercury, that it 
deserves a passing notice. The old tables of this 
planet, Leverrier believed to be defective. He there- 
fore set about a thorough examination of its entire 
theory, and after a rigid scrutiny, deduced a new set 
of tables, from which the places of the planet might 
be predicted with greater precision. 

The transit of Mercury across the sun's disc, 
which occurred on the 8th day of May, 1845, pre- 
sented an admirable opportunity to test the truth of 
the new theory of the young astronomer. Most un- 
happily for his hopes, all observations in Paris were 
rendered impossible by the clouds, which covered the 
heavens during the entire day on which the transit 
took place. While the computer was sadly disap- 
pointed, I was more fortunate, for a pure and trans- 
parent atmosphere favored this, the first astronomical 
observation I ever made. A slight reference to this 
occurrence may be pardoned. For three years I had 
been toiling to complete a most difficult and labori- 
ous enterprise, the erection of an astronomical ob- 
servatory of the first class, in a country where none 
s 2 



210 STRUCTURE OF THE UNIVERSE. 

had ever existed. Amid difficulties and perplexities 
which none can ever know, the work had moved on, 
and at length I had the high satisfaction of seeing 
mounted one of the largest and most perfect instru- 
ments in the world. I had arranged and adjusted its 
complex machinery — had computed the exact point 
on the sun's disc where the planet ought to make its 
first contact — had determined the instant of contact 
by the old tables, and by the new ones of Leverrier, 
and with feelings which must be experienced to be 
realized, five minutes before the computed time of 
contact, I took my post at the telescope to watch the 
coming of the expected planet. After waiting what 
seemed almost an age, I called to my friend how much 
time was yet to pass, and found but one single min- 
ute out of five had rolled heavily away. The watch 
was again resumed. Long and patiently did I hold 
my place, but again was forced to call out, how speeds 
the time? and was answered that there was yet want- 
ing two minutes of the computed time of contact. — 
With steadfast eye, and a throbbing heart, the vigil 
was resumed, and after waiting what seemed an age, 
I caught the dark break which the black body of the 
planet made on the bright disc of the sun. Now ! I 
exclaimed ; and within sixteen seconds of the computed 
time did the planet touch the solar disc, at the precise 
point at which theory had indicated the first contact 
would occur. 

The planet was followed across the disc of the sun, 
round and sharp, and black, and every observation 
confirmed the superior accuracy of the new tables of 
Leverrier. While the old tables were out fully a min- 
ute and a half in the various contacts, those of Le- 



DISCOVERY OF NEW PLANETS. 211 

verrier were in error by only about sixteen seconds as 
a mean. 

The great success of this investigation encouraged 
the young astronomer to accept the difficult task 
which Arago proposed for his accomplishment, and 
he earnestly set about preparing the wa,y for a full 
discussion of the grand problem of the perturbations 
of Uranus. The importance of the subject demanded 
the greatest caution, and having determined to rely 
solely on his own efforts, he at once rejected all that 
had been previously done, and commenced the prob- 
lem at the very beginning. New analytic theories 
were formed; elaborate investigations of the planets 
Jupiter and Saturn, as disturbing bodies, were made, 
and an entire clearing up of all possible causes of 
disturbance in the known bodies of the system was 
laboriously and successfully accomplished, and the in- 
defatigable mathematician finally reached a point 
where he could say, here are residual perturbations 
which are not to be accounted for by any known exist- 
ing body, and their explanation is to be sought beyond 
the present ascertained limits of the solar system. 

As early as the 10th of November, 1845, M. Lever- 
rier presented a memoir to the Royal Academy of 
Sciences in Paris, in which he determined the exact 
perturbations of Jupiter and Saturn on Uranus. This 
was followed by a memoir, read before the academy 
on the 1st of June, 1846, in which he demonstrates 
that it is impossible to render an exact account of the 
perturbations of Uranus in any other way than by 
admitting the existence of a new planet exterior to the 
orbit of Uranus, and whose heliocentric longitude he 
fixes at 325° on the 1st of January, 1847. On the 



212 STRUCTURE OF THE UNIVERSE. 

30th of August, 1846, a third memoir was presented 
to the academy, in which the elements of the orbit of 
the unknown planet are fixed, together with its mass 
and actual position, with greater accuracy, giving on 
the 1st of January, 1847, 326° 32' for its heliocentric 
longitude. Finally, on the 5th of October, 1 847, a fourth 
memoir was read, relative to the determination of the 
plane of the orbit of the constructive planet. 

It is quite impossible to convey, in popular form, 
the least idea of the profound analytic reasoning em- 
ployed by M. Leverrier in this wonderful investiga- 
tion. None but the rarest genius would have dared 
to reach out 1,800,000,000 of miles into unknown re- 
gions of space, to feel for a planet which had displaced 
Uranus by an amount only about equal to four times 
the apparent diameter of the planet Jupiter, as seen 
with the naked eye — a quantity so small that no eye, 
however keen and piercing, without telescopic aid, 
could ever have detected it. Yet from this minute 
basis was the magnificent superstructure to be reared 
which should eventually direct the telescope to the 
place of a new and distant world. To many minds, 
the resolution of such a problem may appear utterly 
beyond the powers of human genius, and without 
one ray of light to illumine the midnight darkness 
which surrounds it to them, they are disposed to re- 
ject the entire subject. An attentive examination of 
the following train of reasoning may at least demon- 
strate that the problem is not quite so hopeless as it 
would at first appear. 

It was not necessary to extend researches to all 
quarters of the heavens indifferently, in an effort 
to find the unknown body. All the planets revolve 



DISCOVERY OF NEW PLANETS. 213 

in planes nearly coincident with the plane of 
the earth's orbit, and more especially do the distant 
ones. Jupiter and Saturn and Uranus revolve in or- 
bits but little inclined to the plane of the ecliptic. — 
Hence, it w T as fair to conjecture that the new planet, 
should it ever be found, would not violate this gen- 
eral law, and a search for it was properly limited to 
a narrow belt near the plane of the earth's orbit. — 
The limits of research were thus brought down to a 
narrow zone, sweeping around the entire heavens in- 
deed, but insignificant in extent, when compared with 
the whole celestial sphere. 

The next point of examination was the probable 
distance of the unknown planet. Here, again, anal- 
ogy came to the aid of Leverrier. The empirical 
law of Bode, already explained in a former lecture, 
showed that the remote planets increased their dis- 
tances by a very simple law. Saturn was twice as 
remote as Jupiter ; Uranus was at double the distance 
of Saturn, and it was fair to conclude that the un- 
known planet would be about twice as far from the 
sun as Uranus. As a first approximation, then, its 
distance was fixed at about 3,600,000,000 of miles 
from the sun. Kepler's law, regulating the ratio be- 
tween the distances and periods of the planets, gave 
at once the time of revolution of the new planet, in 
case its distance had been correctly assumed. In the 
next place, it was fair to conclude that the orbit of 
the new planet, like those of Jupiter, Saturn, and 
Uranus, would not differ greatly from a circle. These 
conjectures were, in some degree, confirmed by a very 
simple train of reasoning with reference to the dis- 
tance of the disturbing body. If it revolved in an 



214 STRUCTURE OF THE UNLVERSE. 

orbit very near to that of Uranus, then its effect on 
Uranus ought to be excessive, when compared with 
its influence on Saturn, which was found not to be 
the case. Again, if it revolved in an orbit very far 
beyond the limit assigned above, its effect on Uranus 
and Saturn would be very nearly the same, which 
was not verified by examination. 

Having thus roughly fixed limits for the orbit of the 
unknown body, the work of the mathematician now 
commences, having for its grand object the determin- 
ation of the true places of the planet sought at some 
given epoch, and such an orbit as will represent the 
perturbations of Uranus in the most perfect manner. 
To exhibit, in some faint degree, the difficulty of this 
investigation, let us conceive that up to the 1st of 
January, 1800, the solar system had consisted only of 
the known bodies, the sun, planets, satellites, and 
comets. The orbits of all the planets are accurately 
ascertained, and their reciprocal influences computed 
and known. The outermost planet, Uranus, revolves 
in its vast orbit obedient to the great law of gravita- 
tion, acknowledging the predominant influence of the 
sun, and swaying more or less to the action of the 
nearest planets, Saturn and Jupiter. Its predicted 
and observed places coincide, and its movement is 
followed with confidence and exactitude. 

With a full and perfect knowledge of the orbit of 
Uranus, let a new planet be created and projected in 
a vast orbit exterior to, and remote from the orbit of 
Uranus. The new body thus added to the system 
would instantly derange the motions of Uranus, caus- 
ing it to recede from the sun, and increasing its mean 
period of revolution. In this case, the total effect of 



DISCOVERY OF NEW PLANETS. 215 

the new planet on Uranus would be perturbation, and 
it would not be quite impossible, even for one not 
skilled in the higher mathematics, to see how the ac- 
tion of the newly created planet on the movements 
of the old one might actually reveal approximately 
the position of the disturbing body. It is manifest 
that when the two planets are in conjunction, or on a 
right line passing through them and the sun, that at 
this configuration the new planet would exert its 
greatest power to drag the old one outward from the 
sun, and if it could be found at what point of its orbit 
the old planet actually receded to its greatest distance 
from the sun, in the same direction, nearly, must the 
disturbing body have been situated at that time. In 
this way, we perceive, one place of the new planet 
might be approximately found, and from its periodic 
time it would be possible to trace it backward or for- 
ward in its orbit, for the present supposed to be 
circular. 

The problem here presented is certainly sufficiently 
difficult, yet its complexity is very far from being 
equal to that presented in nature, and with which the 
French geometer found himself obliged to grapple. — 
Although unknown, the new planet did exist, and for 
ages had silently pursued its unknown orbit round 
the sun. Its influence on Uranus had been ever ac- 
tive, and when the observations on Uranus were 
made, and its places determined, from which its ellip- 
tic elements were to be derived, these very places 
were in part dependent on the action of the invisible 
disturber, and hence a portion of its influence would 
be darkly concealed in the orbit of Uranus ; and to 
divide the entire effect of the new planet on the old 



216 STRUCTURE OF THE UNIVERSE. 

one correctly between the disguised portion and that 
producing real perturbation, was attended with the 
greatest difficulty, and could only be reached by adopt- 
ing certain positive hypotheses. Surrounded by all 
these difficulties, Leverrier worked on, and with con- 
summate art, so constructed his analytical machinery 
as to meet and master every difficulty ; and he finally 
announces to the world the figure of the orbit of his 
imaginary planet, its distance, period of revolution, 
and even the mass of matter it contains. 

These important communications were made to the 
French Academy of Sciences, on the 31st of August, 
1846. On the 18th of the following month, M. Lever- 
rier wrote to his friend M. Galle, of Berlin, requesting 
him to direct his telescope to that point in the heavens 
which his computations had revealed as the one occu- 
pied by the constructive planet. The request was 
readily complied with, and on the very first evening 
of examination, a star of the eighth magnitude was 
discovered, which was evidently a stranger in that 
region, as it was not found on an accurate map of the 
heavens including all stars of that magnitude. The 
following evening was awaited with the deepest in- 
terest, to decide, by the actual motion of the suspected 
star, whether indeed it was the planet so wonderfully 
revealed by the analysis of Leverrier. The night 
came on. Again was the telescope directed to the 
star in question, when lo ! it had moved from its for- 
mer place, in a direction and with a velocity almost 
precisely accordant with the theory of the French 
geometer ! The triumph was perfect — the planet was 
actually found. The new T s of its discovery flew in 



DISCOVERY OF NEW PLANETS. 217 

every direction, and filled the world with astonishment 
and admiration. 

The exceeding accuracy with which its place had 
been predicted, coming within less than one degree of 
its actual position, gave to M. Leverrier the highest 
confidence in the perfection of his analysis, and filled 
with astonishment the oldest and most learned as- 
tronomers. If scepticism had existed with reference 
to the possible solution of so complex a problem — if 
the theory of Leverrier had been regarded as a beau- 
tiful speculation, ingenious and plausible, but vain in 
its practical application, — the actual discovery of the 
planet silenced all cavil, and put to flight every lin- 
gering doubt. 

As if anything were wanting, to give a more posi- 
tive character to the computations of Leverrier, it 
was now found that a young English mathematician, 
Mr. Adams, of Cambridge, had actually accomplished 
the resolution of precisely the same problem, and had 
reached results almost identical with those of the 
French geometer. This astonishing coincidence on 
the part of two computers unknown to each other, 
each starting from the same data, pursuing indepen- 
dent trains of reasoning, and arriving at the same re- 
sults, confirmed, as it would seem, in the fullest man- 
ner, the accuracy of the resolution which had been 
obtained. 

On learning that Leverrier had communicated to 
the Academy of Sciences, in August, 1846, his final 
results, T wrote immediately, requesting the computed 
place of his planet, with such directions as would 
best guide me in a search which I desired to make for 
it with the great refracting telescope of the Cincin- 



218 STRUCTURE OF THE UNIVERSE. 

nati Observatory. But before my letter reached its 
destination, the planet had been found, and the news 
of its discovery soon reached the United States. It 
was almost impossible for me to credit the statement, 
and I was almost disposed to believe that the pre- 
diction of the planet's position had been mistaken for 
its actual discovery. With these conflicting doubts, I 
waited for the coming of night with a degree of anx- 
iety and excitement which may be readily imagined. 
I had no star chart to guide me in my search for the 
planet ; — I had no meridian instrument with which to 
detect it by its motion ; but I was not without hope 
that the power of our great telescope might be suf- 
ficient to select, at once, the planet from among the 
fixed stars, by the magnitude of its disc. 

As soon as the twilight disappeared, the instrument 
was directed to the point in the heavens where the 
planet had been found. I took my place at the finder, 
or small telescope attached to the larger one, and my 
assistant was seated at the great instrument. 

On placing my eye to the finder, four stars of the 
eighth magnitude occupied its field. One of them 
was brought into the field of the large telescope, and 
critically examined by my assistant, and rejected. A 
second star was in like manner examined, and re- 
jected. A third star, rather smaller and whiter than 
either of the others, was now brought to the centre 
of the field of the great telescope, when my assistant, 
exclaimed, "there it is! there is the planet! with a 
disc as round, bright and beautiful as that of Jupiter !" 
There, indeed, was the planet, throwing its light back 
to us from the enormous distance of more than 3,000,- 
000,000 of miles, and yet so clear and distinct, that 



1 1 



DISCOVERY OF NEW PLANETS. 219 

in a few minutes, its diameter was measured, and its 
magnitude computed. 

It is not my intention to follow, critically, the his- 
tory of this wonderful discovery, yet there are some 
facts so remarkable that it would be wrong to pass 
them in silence. From the moment the planet was 
detected in Berlin, it has been observed by all the 
best instruments in the world, with a view of ascer- 
taining how accurately theory had assigned the ele- 
ments of its orbit. In consequence of its very slow 
motion, it became a matter of the utmost importance 
to obtain, if possible, some remote observation made 
by an astronomer who might have entered the place 
of the planet in his catalogue as a fixed star. Mr. 
Adams, of England, led the way in the computation 
of the elements of the orbit of the new planet, from 
actual observation, and was followed by many other 
computers, among them our countryman S. C. Walker, 
then of the Washington Observatory. 

Having obtained an approximate orbit, Mr. Walker 
computed backwards the places of the new planet for 
more than fifty years, and then examined the late 
catalogues, in the hope of finding its place on some of 
them as a fixed star. Among recent catalogues there 
was no success, but in an examination of Lalande's 
catalogue, he found an observation on a star of the 
eighth magnitude, made May the 10th, 1795, which 
was so near the place which his computation assigned 
the planet at the same date, that he was led to sus- 
pect that this star might indeed prove to be the new 
planet. In case his conjecture were true, on turning 
the telescope to the place occupied by the star, it 
would be found blank, as its planetary motion would 



220 STRUCTURE OF THE UNIVERSE. 

have removed it very far from the place which it oc- 
cupied more than fifty years before. The experiment 
having been made, no star could be found, and strong 
evidence was thus presented that Mr. Walker had 
actually found an observation of the new planet, giv- 
ing its position in 1795 ; but in consequence of the 
great discrepancy between the period of M. Leverrier 
and that which would result from a reliance on this 
observation of the new planet Neptune, Mr. Walker's 
discovery was at first received with great hesitation. 
A greater doubt was thrown over the matter from 
the fact that Lalande had marked the observation as 
uncertain, and it was only by reference to the original 
manuscripts preserved in the Royal Observatory of 
Paris that the doubts could be removed. 

The discovery of Mr. Walker was subsequently 
made by Mr. Petersen, of Altona, and the results of 
these astronomers reached Paris on the same day. A 
committee was at once appointed to examine the 
original manuscript of Lalande, when a most remark- 
able discovery was made. This astronomer had ob- 
served a star of the eighth magnitude on the evening 
of the 8th of May, 1795, and on the evening of the 
10th, not finding the star as laid down, but observing 
one of the same magnitude very near the former 
place, he rejects the observation of the 8th of May as 
inaccurate, and enters the observation of the 10th, 
marking it doubtful. 

On close examination, this star proves to be the 
planet Neptune, and by this discovery we are placed 
in possession of observations which render it possible 
to determine the elliptic elements of the new planet 
with great precision. These differ so greatly from 



DISCOVERY OF NEW PLANETS. 221 

those announced by .Leverrier and Adams previous to 
the discovery, that Prof. Pierce, of Cambridge, Mass., 
pronounces it impossible so to extend fairly the lim- 
its of Leverrier's analysis as to embrace the planet 
Neptune ; and that, although its mass, as determined 
from the elongations of its satellite, renders it possi- 
ble to account for all the perturbations of Uranus by 
its action, in the most surprising manner, yet, in the 
opinion of Prof. Pierce, it is not the planet to which 
geometrical analysis directed the telescope. Lever- 
rier rejects absolutely the result reached by the Amer- 
ican geometer, and claims Neptune to be the planet 
of his theory, in the strictest and most legitimate 
sense. 

Time and observation will settle the differences of 
these distinguished geometers, and truth being the 
grand object of all research, its discovery will be 
hailed with equal enthusiasm by both of the dispu- 
tants. In any event, the profound analytic research 
of Leverrier is an ever-during monument to his 
genius, and his name is forever associated with the 
most wonderful discovery that ever marked the career 
of astronomical science. 



t2 



LECTURE VIII. 

THE COMETARY WORLDS. 

The wonderful characteristics which mark the flight 
of comets through space; the suddenness with which 
they blaze forth ; their exceeding velocity, and their 
terrific appearance ; their eccentric motions, sweeping 
towards the sun from all regions and in all directions, 
have rendered these bodies objects of terror and dread 
in all ages of the world. While the planets pursue 
an undeviating course round the sun, in orbits nearly 
circular, and almost coincident with the plane of the 
earth's orbit, all revolving harmoniously in the same 
direction, the comets perform their revolutions in 
orbits of every possible eccentricity, confined to no 
particular plane, and moving indifferently in accord- 
ance with, or opposed to, the general motion of the 
planets. They come up from below the plane of the 
ecliptic, or plunge downwards towards the sun from 
above, sweep swiftly round this their great centre, 
and with incredible velocity wing their flight far into 
the fathomless regions of space, in some cases never 
again to reappear to human vision. 

In the early ages of the world, superstition regarded 
these wandering fiery worlds with awe, and looked 
upon them as omens of pestilence and war; and in- 
deed, even in modern times, no eye can look upon the 
fiery train spread out for millions of miles athwart 

( 223 ) 



224 STRUCTURE OF THE UNIVERSE. 

the sky, and watch the eccentric motions of these 
anomalous objects, without a feeling of dread. The 
movements of the planets inspire confidence. They 
are ever visible, and true to their appointed times, 
while the comet, erratic in its course, bursts suddenly 
and unannounced upon the sight, and no science can 
predict in the outset its uncertain track — whether it 
may plunge into the sun, or dash against one of the 
planetary systems, or even come into collision with 
our own earth, is equally uncertain, until after a suf- 
ficient number of observations shall have been made 
to render the computation of the elements of its orbit 
possible. 

Previous to the discovery of the law of universal 
gravitation, comets were looked upon as anomalous 
bodies, of whose motions it was quite impossible to 
take any account. By some philosophers they were 
regarded as meteors kindled into a blaze in the earth's 
atmosphere, and when once extinguished they were 
lost forever. Others looked upon them as permanent 
bodies, revolving in orbits far above the moon, and 
reappearing at the end of long but certain intervals. 
When, however, it was discovered that, under the in- 
fluence of gravitation, any revolving world might de- 
scribe either of the four curves, the circle, ellipse, para- 
bola or hyperbola, it at once became manifest that the 
eccentric movements of the comets might be perfectly 
represented by giving to them orbits of the parabolic 
or hyperbolic form, the sun being located in the focus 
of the curve. According to this theory, the comet 
would become visible in its approach to its perihelion, 
or nearest distance from the sun, — would here blaze 
with uncommon splendor, and in its recess to the re- 



THE COMETARY WORLDS. 225 

mote parts of its orbit, would gradually fade from the 
sight, relaxing its speed, and performing a large pro- 
portion of its vast curve far beyond the reach of hu- 
man vision. 

Such was the theory of Newton, and such were the 
fair deductions from the great law of nature which he 
had revealed to the world. He awaited with deep 
interest the appearance of some brilliant comet, whose 
career he might trace, in the full confidence that ob- 
servation would confirm the truth of his bold hypothe- 
sis. Fortunately, his impatience was soon gratified. 
In the year 1680 a most wonderful comet made its 
appearance, which, by its splendor and swiftness, ex- 
cited the deepest interest throughout the world. It 
came from the regions of space immediately above 
the ecliptic, and plunging downwards with amazing 
velocity, in a direction almost perpendicular to this 
plane, it appeared to direct its flight in such manner 
that it must inevitably plunge directly into the sun. 
This was not, however, the case. Increasing its ve- 
locity as it approached the sun, it swept round this 
body with the speed of a million of miles an hour, 
approaching the sun to within a distance of its sur- 
face of a sixth part of the sun's radius. It then 
commenced its recess, throwing off a train of light 
which extended to the enormous distance of 100,000,- 
000 of miles. With the swiftness of thought almost, 
it swept away from the sun, and was gradually lost 
in the distant regions of space whence it came, and 
has never since been seen. Such were the general 
characteristics of the body to whose rapid motions 
Newton attempted to apply the law of universal 
gravitation. 



226 STRUCTURE OF THE UNIVERSE. 

Its positions were marked with all the accuracy 
which the instruments then in use permitted, and it 
was found that a parabolic curve could be constructed 
which would embrace all the places of the comet. — 
The great eccentricity of its orbit, and its vast period, 
amounting to nearly six hundred years, gave to the 
comet great interest, but rendered it an unfit object 
for successful analytic researche. The great English 
astronomer, Halley, had studied it with the closest 
care, and with a rigid application of Newton's theory, 
he reached results quite as satisfactory as the circum- 
stances of the case rendered possible. 

Fortunately, in 1682, another comet made its ap- 
pearance, to the study of which Halley devoted him- 
self with a zeal and success which has justly stamped 
his name on this remarkable body ; and as our limits 
forbid an extensive investigation of the history and 
theory of comets, I propose to examine this one with 
that degree of detail which may convey some idea of 
the limits of human knowledge in this complicated 
department of science. 

At the suggestion of Newton, Halley had searched 
all ancient and modern records, for the purpose of 
rescuing any historical details touching the appearance 
and aspect of comets, from the primitive ages down to 
his own time. On the appearance of the comet of 
1682, he observed its positions with great care, and 
with wonderful pains computed the elements of its 
orbit. He found it moving in a plane but little in- 
clined to the ecliptic, and in an ellipse of very great 
elongation. In its aphelion, it receded from the sun 
to the enormous distance of 3,400,000,000 of miles. — 
He discovered that the nature of its orbit was such 



THE COMETARY WORLDS. 227 

as to warrant the belief that the comet would return 
at regular intervals of about seventy-five years, and 
recurring to his historical table of comets, he found it 
possible to trace it back with certainty several hun- 
dred years, and with probability even to the time of 
the birth of Mithridates, one hundred and thirty years 
before Christ. At this, its first recorded appearance, 
its magnitude must have been far beyond anything 
subsequently seen, as its splendor is said to have sur- 
passed that of the sun. 

In the years 248, 324, and 399 of the Christian era, 
remarkable comets are recorded to have appeared, 
and the equality of interval corresponds well with Hal- 
ley's comet. In the year 1006, it presented a frightful 
aspect, exhibiting an immense curved tail in the form 
of a scythe. In 1456, its appearance spread conster- 
nation through all Europe, and led to most extrava- 
gant acts on the part of the reigning pontifF, who 
actually instituted a form of prayer against the bale- 
ful influence of the comet, and thus increased the 
terrors of the ignorant and superstitious. The comet 
appeared with certainty in 1531, and again in 1607, 
and from an examination of all the facts, and with full 
confidence in his computations, Halley ventured the 
bold prediction that this same comet would reappear 
about the close of 1758, or the beginning of 1759. 

This was certainly the most extraordinary predic- 
tion ever made, and the distinguished philosopher, 
knowing that he could not live to witness the verifica- 
tion of this prophetic announcement, expresses the 
hope that when the comet shall return, true to his 
computed period, posterity will do him the justice to 
remember that this first prediction was made by an 



228 STRUCTURE OF THE UNIVERSE. 

Englishman. In the age when these investigations 
were made, the theory of comets was in its infancy, 
and it is believed by those competent to form a just 
opinion, that Halley was the only man living who 
could have computed the orbit of his comet. 

As the period approached for the verification of this 
extraordinary announcement, the greatest interest was 
manifested among astronomers, and efforts were made 
to predict its coming with greater accuracy, by com- 
puting the disturbing effects of the larger planets 
within the sphere of whose influence the comet might 
pass. This was a new and difficult branch of astro- 
nomical science, and it would be impossible to convey 
the least idea of the enormous labor which was gone 
through by Clairaut and Lalande, in computing the 
perturbations of this comet through a period of two 
revolutions, or one hundred and fifty 3 r ears. 

" During six months," says Lalande, "we calculated 
from morning till night, sometimes even at meals, — 
the consequence of which was that I contracted an 
illness which changed my constitution during the re- 
mainder of my life. The assistance rendered by 
Madame Lepaute was such, that without her we never 
should have dared to undertake the enormous labor, 
in which it was necessary to calculate the distance 
of each of the two planets, Jupiter and Saturn, from 
the comet, separately for every degree, for one hun- 
dred and fifty years." 

Amid all these difficulties, the computers toiled on, 
until finally, the period coming on rapidly for the 
comet's return, they were forced to neglect some mi- 
nor irregularities, and Clairaut announced that the 
comet would be retarded one hundred days by the in- 



THE COMETARY WORLDS. 229 

fluence of Saturn, and five hundred and eighteen days 
by the action of Jupiter ; — he therefore fixed its peri- 
helion passage for the 13th of April, 1759, stating, at 
the same time, that the result might be inaccurate by 
some thirty days either way, in consequence of being 
pressed for time, and his having neglected certain 
small perturbations. 

These results were presented to the Academy of 
Sciences on the 14th of November, 1758, and on the 
25th of the following December, George Palitch, an 
amateur peasant astronomer, caught the first glimpse 
of the long expected wanderer, which, after an ab- 
sence of three-quarters of a century, once more re- 
turned to crown with triumph the great English as- 
tronomer who first foretold its period, and the eminent 
French mathematicians who had actually computed 
its perihelion passage, to within nineteen days, in 
seventy-six years ! 

Here, then, was a new world added to the solar 
system, linked to the sun by the immutable law of 
gravitation ; sweeping out into space to the amazing 
distance of 3,800,000,000 of miles ; lost to the gaze 
of the most powerful telescope, and yet traced by the 
human mind through its vast and hidden career, with 
an accuracy and precision from which there was no 
escape. The very small error of nineteen days in 
Clairaut's computation strikes us with astonishment, 
when we remember the imperfect state of analytical 
science at that day, and the fact that tw T o planets, 
Uranus and Neptune, which have since been dis- 
covered, were then not even suspected to have any 
existence. 

The magnificent display which had marked some 
U 



230 STRUCTURE OF THE UNIVERSE. 

of the early returns of Halley's comet, and which 
produced such consternation among all classes, the 
educated as well as the ignorant, were not presented 
during its appearance in 1758. This was owing, in 
part, to the unfavorable position of the earth in its 
orbit at the time of the comet's perihelion passage. — 
The vast trains of light which are sometimes seen to 
accompany comets, are only displayed in their ap- 
proach to the sun. They attain their greatest splen- 
dor while the comet is in the act of passing its peri- 
helion, and as it recedes into space, the tail fades 
away, from two causes — an actual diminution from 
condensation, and an apparent decrease on account 
of increased distance. 

As the comet, when near the sun, moves with in- 
creased velocity, it occupies, in general, only a short 
period in passing through the limits of distance from 
the sun within which any train of light is developed. 
It may happen that at one return of the same comet, 
the earth may occupy a point in her orbit, during its 
perihelion passage, which may be very near to the 
comet, and thus afford an opportunity of witnessing 
its appearance at a short distance ; while, on the 
next return, the earth being at a remote part of its 
orbit while the comet is passing the sun, it may be 
seen only with great difficulty, or even become quite 
invisible. If, therefore, astronomers were obliged to 
depend upon a uniform physical appearance of 
comets at their successive returns, to determine their 
identity, there would scarcely be the slightest chance 
of ever recognizing even a single one among the 
many thousands which are sweeping through the re- 
gions of space 



THE COMETARY WORLDS. 231 

The interval from 1759 to 1835, when Halley's 
comet ought to make its next appearance, had wit- 
nessed extraordinary changes in astronomy. The 
methods for computing planetary perturbations had 
been greatly improved ; the planet Uranus had been 
added to the system, and more accurate masses of the 
larger planets, especially of Saturn, had been ob- 
tained. Twenty-five years before the close of the 
comet's period, its return commenced to interest as- 
tronomers, and prizes were offered by two academies 
for the most perfect theory of this remarkable body. 
Baron Damoiseau and M. Pontecoulant were the suc- 
cessful competitors for the two prizes, although sev- 
eral other astronomers undertook and completed the 
task of computing the planetary perturbations. Al- 
though the computers differed slightly in the time of 
the perihelion passage, the difference was due to the 
imperfection of the data employed, rather than to any 
defect in the methods of computation. 

For the expected return in 1835, not only was the 
perihelion passage computed, but the exact route of 
the comet among the fixed stars was wrought out 
with surprising accuracy, and the precise point to- 
wards which the telescope must be directed at the 
time when the comet would first attain the limits of 
visibility. Strange and almost incredible as it must 
appear, guided by these predictions, M. Dumouchel, 
director of the observatory of the Roman College, on 
the evening of the 5th of August, 1835, fixed his tel- 
escope in the position indicated by computation, and, 
on placing his eye to the tube, lo ! the comet ap- 
peared, as a faint and almost invisible stain of light 
on the deep blue of the heavens. 



232 STRUCTURE OF THE UNIVERSE. 

Again did science triumph, in the most remarkable 
manner, and the computed orbit of the comet was 
followed by it with the most surprising accuracy. — 
The perihelion passage was predicted to within nine 
days of its actual occurrence, a most astonishing ap- 
proximation to the truth, when it is remembered that 
this body, far as it penetrates into space, never, even at 
the remotest point of its orbit, escapes from the sen- 
sible influence of the planet Jupiter. Moreover, at 
that time, the new planet, Neptune, was unknown, 
and its influence over the comet could not be taken 
into account. 

It is interesting to remark the confidence with 
which astronomers relied on Halley's comet for infor- 
mation relative to those bodies, which inhabited the 
regions of space exterior to the known limits of the 
solar system. It was urged by every computer that 
the orbit of this comet would one day come to be so 
perfectly known, that the perturbations due to the 
recognized bodies of the solar system might be com- 
puted with such precision, that the residual perturba- 
tions might be pronounced to be the effect of un- 
known planets or comets circulating in the distant 
regions of space. This conjecture has been realized, 
although by different means, and a planet is now 
added to our system, which revolves in an orbit so 
vast as to circumscribe within its limits the entire 
sweep of the comet ; and as the orbits of Neptune 
and Halley's comet are inclined under an angle of 
only 15° or 16°, a time will come when the perturba- 
tions experienced by the comet when at its aphelion, 
from Neptune's influence, may be so great that, but 
for the fortunate discovery of the cause, would have 



THE COMETARY WORLDS. 233 

falsified, in the most unaccountable manner, the pre- 
dictions of the comet's return by future astronomers. 
During its late return, the finest telescopes in the 
world were employed in a critical examination of the 
physical condition of Halley's comet. Elaborate 
drawings have been made by M. Struve, the dis- 
tinguished director of the Imperial Observatory at 
Pulkova, Russia, with the grand refracting telescope 
under his charge, and also by Sir John Herschel, 
at the Cape of Good Hope, with a twenty feet reflec- 
tor of superior power. To these beautiful drawings 
reference will be made hereafter. 

The most wonderful changes in the magnitude and 
figure of the comet were observed to take place from 
night to night, and almost perceptible from hour to 
hour under the eye of the observer. The nucleus 
was sometimes seen sharp and strongly condensed, 
with more or less nebulous light around it. Some- 
times a luminous crescent became distinctly visible 
near the nucleus, giving to the comet a most extra- 
ordinary appearance. At one time M. Struve saw 
the comet attended by two delicately shaped appen- 
dages of light of a most graceful form, the one pre- 
ceding, the other following the nucleus of the comet. 
At other times it was seen to be surrounded by a sort 
of semi-circular veil, which, extending backwards, 
was lost in a double train of light, which flung itself 
out to a vast distance from the body of the comet. 

Leaving, for the present, the consideration of the 
physical constitution of these eccentric bodies, we 
proceed to the examination of a remarkable object 
which bears the name of Encke's comet, in conse- 
quence of the discovery by this learned astronomer 
u 2 



234 STRUCTURE OF TFJE UNIVERSE. 

that its orbit was elliptical, and its period of revolu- 
tion so short as to fall fairly within the limits of per- 
petual examination. 

In 1818, a comet was discovered by Pons, not at all 
remarkable for its magnitude, for it was even invisible 
to the naked eye, but when the attempt was made to 
represent its places by a parabolic orbit, which had 
thus far been invariably applied to the comets, it was 
found impossible to assign any elongated orbit which 
would embrace the observed positions of the comet. 
After a very elaborate investigation, Professor Encke 
at length reached the conclusion that the orbit was 
not a parabola, but an ellipse of comparatively small 
dimensions, and that this comet was actually revolv- 
ing around the sun in a period of about three years. 
This discovery excited a great deal of interest, for it 
was the first in which a short period had been detect- 
ed, and efforts were at once made to identify the new 
member of the solar system in its preceding revolu- 
tions. Olbers determined its identity with a comet 
which appeared in 1795, and subsequently ascertained 
that another, which had been observed but twice in 
1786, and from which observations no elements could 
be computed, could be no other than the new comet 
of that period. In this way, observations on this in- 
teresting object were obtained, stretching through 
some thirty-three years, or about ten of its revolu- 
tions. This extended series of observations furnished 
the data for a critical examination of the elements of 
the comet's orbit, and Prof. Encke, having discussed 
them with elaborate care, reached the astonishing 
conclusion that the magnitude of the orbit was grad- 
ually diminishing, the periodic time growing shorter 



THE COMET ARY WORLDS. 235 

from revolution to revolution, and that the comet was 
certainly falling nearer and nearer to the sun ! 

To account for this extraordinary phenomenon, the 
learned astronomer, having exhausted all causes 
known to exist in the solar system, finally, with much 
hesitation, announced the theory of the comet's motion 
in a resisting medium. The existence of such a me- 
dium was in direct opposition to all the received doc- 
trines of astronomy, and the absolute necessity for its 
use in this instance was looked upon by astronomers 
with feelings of strong distrust. But Encke argued 
that such a medium might exist, of such exceeding te- 
nuity as not sensibly to affect the movements of the 
ponderous planets, while a filmy mass of vapor, such 
as this comet undoubtedly was, might be very sensibly 
retarded in its original velocity, which would diminish 
continually the centrifugal force, and give to the cen- 
tral attraction of the sun a constantly increasing 
power, which would produce precisely the phenom- 
ena exhibited by the comet. 

With these views, Encke predicted the reappear- 
ance of the comet in 1822. In consequence of its 
great southern declination at that period, it escaped 
all the European observers, and was only seen at 
Paramatta, by Rumker. The approach to the sun 
was in some degree confirmed by these observations, 
but it was impossible to reconcile all the observations 
with the hypothesis of a medium of given density. — 
The return in 1825 was not favorable for deciding the 
question, which had now become one of the deepest 
interest. 

Its reappearance in 1828-9 was awaited with great 
anxiety by the friends and opponents of the new 



236 STRUCTURE OF THE UNIVERSE. 

theory. The comet came round, and passed its peri- 
helion approximately in accordance with the predic- 
tions, but the discrepancies from 1819 up to 1829, 
with any theory, were so great, as to give much per- 
plexity to those engaged in the computations. After 
long and- patient examination, the cause of this diffi- 
culty was finally detected. The plane of the comet's 
orbit makes but a small angle with the orbit of Jupi- 
ter, and when the comet is in aphelion, or farthest 
from the sun, it always approaches very near to the 
path described by the planet. 

A time may then come when Jupiter shall be in the 
act of passing that part of its orbit very near to the 
aphelion point of the cometary ellipse, while the 
comet occupies its aphelion, bringing these bodies 
into close proximity, and producing excessive pertur- 
bations in the movements of this almost spiritual 
mass. Such, indeed, was the configuration between 
the returns of 1819 and 1829, on which occasion the 
comet was delayed in its return to its aphelion by 
nearly nine days, by the powerful attraction of Jupi- 
ter. Under these circumstances, any error in the as- 
sumed mass of the planet would exhibit itself in an 
exaggerated form in the perturbations of the comet. 
But it was believed in the outset of this investigation, 
that the mass of Jupiter, employed by Laplace in 
his theory of the planets, and computed by Bouvard, 
could be relied on as accurate. Indeed, Laplace had 
applied the calculus of probabilities, and had found 
that there was but one chance out of eleven millions 
that the mass he had adopted could be in error by the 
one hundredth part of its value. 

Suspicion, however, having been aroused with ref- 



THE COMETARY WORLDS. 237 

erence to the mass of Jnpiter, efforts were at once 
commenced to sift thoroughly the matter, and three 
different computers of high reputation undertook the 
determination of Jupiter's mass by different processes. 
Encke obtained a mass from the perturbations of the 
small planet Vesta, Nicolai from the perturbations of 
Juno, and Airy reexamined the original measures of 
the elongations of Jupiter's satellite, made new meas- 
ures, and thus obtained new data for the resolution 
of the problem of Jupiter's mass. The results ob- 
tained by the three astronomers agreed in a most re- 
markable manner, and proved incontestably that La- 
place's value of the mass of this planet was in error 
more than four times the hundredth part of its value, 
and that, instead of requiring 1,070 globes of the mag- 
nitude of Jupiter to balance the sun, only 1,049 were 
necessary. 

With the new mass of Jupiter it seemed possible, 
by admitting a resisting medium, to account for all 
the perturbations of Encke's comet, and for a time 
this theory seemed to receive greater consideration 
from distinguished men. The appearance of Halley's 
comet in 1835 again threw great doubt over the sub- 
ject, for it was found impossible to reconcile the move- 
ments of the two comets with any assumed density 
of a resisting medium. Some have been disposed to 
adopt the idea that the revolution of the planets, for 
ages, in the same direction, in this supposed ethereal 
fluid, has impressed upon it a certain amount of mo- 
tion in the same direction, and that those comets 
which chance to revolve with the current will be 
found to be operated upon differently from those 



238 STRUCTURE OF THE UNIVERSE. 

which may happen to come into our system in a di- 
rection opposed to the current. 

I confess, frankly, that my own mind has always 
revolted against the doctrine of a resisting fluid. — 
There are so many ways in which the single phenom- 
enon of the gradual approach of Encke's comet to 
the sun may be accounted for, without resorting to an 
hypothesis which involves the entire destruction of 
the planetary system, whose perpetuity has been so 
effectually provided for by the great Architect of the 
universe, that it would require the most unequivocal 
testimony to secure the full consent of my own mind 
to the adoption of this remarkable theory. It is 
proper, however, to say, that it has long been received 
with favor by men to whose judgment I am generally 
disposed to yield with implicit confidence. 

Leaving the further consideration of this subject 
for the present, we proceed to the examination of an- 
other comet of short period, which has excited great 
attention, especially in its recent return. As early as 
1805, Prof. Gauss, in computing the elements of the 
orbits of the comets of that year, found one which 
seemed to complete its revolution in about six years. 
This comet, however, was lost sight of, and it was 
not until 1826 that M. Biela discovered the same comet 
on its return to its perihelion. This discovery appears 
to have been the result of computation, but how far 
the investigation was carried, I have never been able 
to learn. 

The same object was also discovered by M. Gam- 
bart about the same time, who, on fixing its elements, 
found that it performed its revolution about the sun 
in an ellipse, with a period of six and three-quarter 



THE COMETARY WORLDS. 239 

years. This comet, like Encke's, is only to be seen 
with the telescope. It presents no solid, or even well 
defined nucleus, and appears to be a mere vapory 
mass, of exceeding tenuity. Taking into account 
the disturbing influence of Jupiter, the returns of 
Biela's comet, as predicted, agreed well with observa- 
tion, and gave confidence in the theory on which the 
predictions were founded. 

The return in 1832 excited the liveliest interest 
throughout the civilized world, in consequence of the 
fact that it was discovered from computation, that on 
the night of the 29th of October, this comet would 
pass a little within the earth's orbit, and those unac- 
quainted with the subject received the impression 
from this announcement, that the earth and comet 
would come into collision, producing the most terrific 
consequences. Such was the consternation excited, 
throughout the city of Paris especially, that the Acad- 
emy of Sciences found it necessary to give to the sub- 
ject their serious attention, and finally gave the mat- 
ter in charge to M. Arago, who produced an elaborate 
report on the subject of comets generally, which 
served to calm the popular apprehension, and has 
proved to be a valuable addition to our knowledge on 
this difficult subject. 

In this report, M. Arago showed that the comet 
would indeed cross the earth's track at the time pre- 
dicted, but at the moment of crossing, the earth would 
be some fifty-five millions of miles distant from the 
point occupied by the comet, and could not experience 
the slightest possible influence from such a body, at 
such a distance. 

If the comet had been delayed in its approach for 



240 STRUCTURE OF THE UNIVERSE. 

thirty days, by any disturbing cause, then, indeed, the 
earth and comet would have filled at the same time 
the point where their orbits intersect, and the dreaded 
collision would have taken place. The consequences 
of such a shock it is impossible to conjecture, but 
reasoning from the known physical condition of the 
comet, none of the terrible disasters so generally an- 
ticipated would have occurred. The exceeding rarity 
of the matter composing this body may be inferred 
from the statements of Sir John Herschel. " It 
passed," says he, " over a small cluster of most minute 
stars of the 16th and 17th magnitude; and when on 
the cluster presented the appearance of a nebula re- 
solvable, and partly resolved, the stars of the cluster 
being visible through the comet. A more striking 
proof could not have been offered of the extreme 
translucency of the matter of which the comet con- 
sists. The most trifling fog would have effaced this 
group of stars, yet they continued visible through a 
thickness of cometic matter which, calculating on its 
distance and apparent diameter, must have exceeded 
50,000 miles, at least towards its central parts. That 
any star of the cluster was centrally covered, is indeed 
more than I can assert ; but the general bulk of the 
comet might be said to have passed centrally over 
the group" 

Such is the nature of the body from whose contact 
the ignorant apprehended the most fearful convul- 
sions. Gibers, who studied the subject with great 
care, was disposed to think that in case the earth had 
passed directly through the comet, no inconvenience- 
would have occurred, and no change beyond a slight 
influence on the climate would have been experienced. 



THE COMET ARY WORLDS. 241 

It is useless to speculate with reference to the 
probable consequences of a collision, which there is 
scarcely one chance in millions can ever occur. — 
Science has as yet discovered no guarantee for any 
planet against the possible shock of a comet ; but an 
examination of the delicate adjustments of our own 
system, and those of Jupiter and Saturn, would seem 
to indicate to us that in all past time no derangement 
has ever occurred from such a cause. 

The last return of Biela's comet was marked by a 
phenomenon unexampled, so far as I know, in the his- 
tory of these wandering bodies. True to the predic- 
tions of Santini, the comet first became visible on 
the evening of the 26th of November, 1845, and in 
the precise point which had been assigned by theory. 
DeVico, the director of the observatory at Rome, was 
the first to catch a glimpse of the expected comet. — 
Nothing remarkable in its appearance was noticed, 
until about the 29th of December, when Mr. E. C. 
Herrick, of New Haven, pointed out to several friends 
what he regarded to be a sort of anomalous tail, but 
shooting out from the head of the comet in a direction 
entirely at variance with the usually received theory, 
that the tail is always opposite to the sun. In this 
supposed tail a kind of knot was noticed, brighter and 
more condensed than any other part. Owing to in- 
sufficient optical power, the true character of the 
phenomenon was not fairly detected by Mr. Herrick. 

On the night of the 12th of January, 1848, Lieut. 
Maury, in charge of the observatory at Washington 
City, discovered that what had hitherto appeared as a 
single body, was actually composed of two distinct and 
separate comets ! This most extraordinary fact was 
V 



242 STRUCTURE OF THE UNIVERSE. 

immediately announced, and the double character 
was observed at all the principal observatories in 
Europe and the United States. There can be no 
doubt whatever as to the reality of the appearance. 
The comet actually became double, and the two parts, 
bound together by some inscrutable bond, continued 
their swift journey through space, pursuing almost 
exactly the route predicted for the single comet. 

From measures obtained by Prof. Challis, of Cam- 
bridge, England, on the 23d of January, 1846, the 
two comets were separated from each other by a dis- 
tance equal to about one-thirteenth the apparent di-. 
ameter of the sun. On the 28th of the same month, 
Sir John Herschel records the following notices : — 
" The comet was evidently double, consisting of two 
distinct nebulae, a larger and a smaller one, both 
round, or nearly so, — the one in advance faint and 
small, and not much brighter in "the middle ; the one 
which followed nearly three times as bright, and one 
and a half times larger in diameter, and a good deal 
brighter in the middle, with an approach to a stellar 
point." 

On the evening of the 9th of February, having re- 
turned to the observatory at Cincinnati, after an ab- 
sence of more than two months, I had an opportunity 
of beholding, for the first time, these wonderful ob- 
jects, with the twelve inch refractor. The moon was 
nearly full, and yet the comets were distinctly visible, 
both included within the limits of the field of view 
of the instrument, and separated from each other by 
a distance equal to about the eighth part of the sun's 
diameter. The preceding comet was evidently the 
brighter of the two. 



THE COMETARY WORLDS. 243 

Clouds prevented a continuous examination of the 
comets from night to night, but on the evening of the 
21st of February, I was surprised to find a remarka- 
ble change in the relative brilliancy of the two parts. 
On that evening the following comet was very deci- 
dedly brighter than its companion, and from observa- 
tions made elsewhere, the change of relative bright- 
ness seems to have been effected about the 13th or 
14th of February. The change was observed by 
Prof. Encke, of Berlin, as early as the 14th. On the 
evening of the 21st of February, both comets exhib- 
ited distinct trains of light, extending from the sun, 
and in directions parallel to each other. The centre 
of the nucleus of each comet was brighter than the 
surrounding portions, but there was no stellar point 
visible. The nebulosity of the two points did not 
intermingle. 

The distance between the comets increased from 
day to day, until, on the 25th of February, they were 
separated by an amount equal to 445 seconds of arc, 
or between a fourth and fifth part of the sun's diame- 
ter. A part of the increase of distance was only 
apparent, arising from the approach of the comets to 
the earth, but the comets were actually receding from 
each other while pursuing their rapid flight through 
space. 

Neither did the line joining the central points of the 
comets remain parallel to itself. From the 23d of 
January to the 11th of February, this line shifted its 
position by an amount of angular motion equal to 8°, 
as is shown by a comparison of the measures of 
Challis and Encke. By the 21st of February, this 
angular motion had been nearly destroyed by a retro- 



244 STRUCTURE OF THE UNIVERSE. 

grade movement, and thus the comets were seen to 
oscillate about each other, according to some mysteri- 
ous law which has never been revealed. Such is a 
brief sketch of the phenomena presented by Biela's 
comet in its late return. Its next appearance will be 
looked for with deep interest, to confirm or destroy 
certain theories which have been propounded to ex- 
plain its duplex character. 

While the periods of the comets which we have 
thus far considered are comparatively short, those of 
others which have visited our system have been ascer- 
tained to extend to many thousands of years. The 
great comet of 1811, one of the most brilliant of 
modern times, in consequence of its remaining visible 
for nearly ten months, gave ample opportunity for the 
investigation of the elements of its orbit. After a 
careful investigation, M. Argelander fixes its period 
of revolution at 2,888 years. Bessel had examined 
the same subject previously, and probably with less 
attention, but obtained a period even greater than 
Argelander's, amounting to 3,383 years. 

The comet of 1807 also occupied the attention of 
Bessel. A long series of observations furnished the 
data for computing its elements. The periodic time 
was fixed at 1,543 years. These computations are 
necessarily only approximate. The difficulty of ob- 
taining accurately the periodic time increases with 
the length of the period, and all that can be done is 
to fix a limit below which it cannot fall. These vast 
periods give to us the means of learning somewhat 
of the great distance to which these objects penetrate 
into space. The comet of 1811, having a period 
probably three thousand times greater than that of 



THE COMETARY WORLDS. 245 

our earth, must revolve at a mean distance from the 
sun of more than 80,000,000,000 of miles, and in con- 
sequence of its very near approach to the sun at its 
perihelion, its greatest distance cannot fall below 
160,000,000,000 of miles ! 

Great as this distance is, it is perfectly certain that 
there are many comets which revolve in orbits far 
more extensive than the one described by the comet 
of 1811. Indeed, there seems to be no limit to the 
distance to which these bodies may sweep outward 
from the sun; and their return depends simply on the 
fact whether they recede so far as to fall within the 
attractive influence of some other sun, towards which 
they begin to urge their flight, and through whose sys- 
tem of planets they carry the same apprehensions of 
danger which have been caused in our own. 

In reflecting on these singular objects, we are led to 
inquire what they are, whence their origin, and by what 
laws are the vast trains of light which occasionally 
distinguish them developed ? Arago divides comets 
into three classes, with reference to their physical con- 
stitution. He thinks they occasionally appear round, 
and with well defined planetary discs, showing them 
to be soild opaque bodies, in all respects resembling 
planets, and only differing from these in the great ec- 
centricity of their orbits. In confirmation of this 
opinion, he asserts that comets have been seen to 
transit the sun, and when passing between this lumi- 
nary and the eye of the spectator, they appear round 
and black, like the planets Mercury and Venus, when 
seen under the same circumstances. An example of 
this kind occurred on the 18th of November, 1826, 
when the transit of a comet across the sun was wit- 
v 2 



246 STRUCTURE OF THE UNIVERSE. 

nessed by two persons, widely separated from each 
other. 

A second class of comets comprehends those in 
which there is a nucleus, but devoid of opacity, per- 
mitting the light to penetrate through even that por- 
tion which may possibly be solid. The third class, 
and that by far the most numerous, comprehends 
those comets destitute, entirely, of any solid nucleus, 
consisting of matter so attenuated as to compare 
fairly with nothing of which we have any knowledge 
on the earth's surface. The comets named for Encke 
and Biela appear to belong to this class ; and even 
Halley's comet, according to the opinion of Sir John 
Herschel, seems, at its last return, to have been en- 
tirely turned into vapor in its perihelion passage. 

No theory, with the exception of Laplace's nebular 
hypothesis, has ever been framed to explain the ori- 
gin of these wandering bodies. This is not the place 
to enter into a full development of this subject. — A 
few hints only can be given. Laplace, following up 
the speculation of Sir William Herschel, applied the 
theory of that astronomer to the formation of the 
solar system, comprehending the comets, as well as 
the planets and their satellites. This theory supposes 
that the original chaotic condition of the matter of 
all suns and worlds was nebulous, like the matter 
composing the tails of comets. Under the laws of 
gravitation, this nebulous fluid, scattered throughout 
a.11 space, commences to condense towards certain 
centres. The particles moving towards these central 
points, not meeting with equal velocities, and in op- 
posite directions, a motion of rotation is generated in 



THE COMETARY WORLDS. 247 

the entire fluid mass, which, in figure, approximates 
the spherical form. 

The spherical figure once formed, and rotation com- 
menced, it is not difficult to conceive how a system 
of planets might be produced from this rotating mass, 
corresponding, in nearly all respects, to the charac- 
teristics which distinguish the planets belonging to 
our own system. If, by radiation of heat, this nebu- 
lous mass should gradually contract in size, then a 
well known law of rotating bodies would insure an 
increased velocity of rotation. This might continue 
until the centrifugal force, which increases rapidly 
with the velocity of the revolving body, would finally 
come to be superior to the force of gravity at the 
equator, and from this region a belt of nebulous fluid 
would thus be detached, in the form of a ring, which 
would be left in space by the shrinking away of the 
central globe. The ring thus left would generally 
coalesce into a globular form, and thus would present 
a planet with an orbit nearly, if not quite circular, 
lying in a plane nearly coincident with the plane of 
the equator of the central body, and revolving in its 
orbit in the same direction in which the central globe 
rotates on its axis. 

As the globe gradually contracts, its velocity of ro- 
tation continually increasing, another ring of matter 
may be thrown off, and another planet formed, and 
so on, until the cohesion of the particles of the cen- 
tral mass may finally be able to resist any further 
change, and the process ceases. 

The planetary masses, while in the act of cooling 
and condensing, may produce satellites in the same 
manner, and by the operation of the same laws by 



248 STRUCTURE OF THE UNIVERSE. 

which they were themselves formed. Strange and 
fanciful as this speculation may appear, there are 
many facts which tend strongly to give it more than 
probability. It accounts for all the great features of 
the solar system, which, in its organization, presents 
the most indubitable evidence that it has resulted 
from the operation of some great law. 

The sun rotates on an axis in the same direction 
in which the planets revolve in their orbits ; the 
planets all rotate on their axes in the same direction ; 
they all circulate around the sun in orbits nearly circu- 
lar, in the same direction, and in planes nearly coinci- 
dent with the plane of the sun's equator. The satel- 
lites of all the planets, with one single exception, 
revolve in orbits nearly circular, but little inclined to 
the equators of their primaries, and in the same direc- 
tion as the planets. So far as their rotation on axes 
has been ascertained, they follow the general law. — 
In one instance alone we find the rings of matter 
have solidified in cooling, without breaking up or be- 
coming globular bodies. This is found in the rings 
of Saturn, which present the very characteristics 
which would flow from their formation according to 
the preceding theory. They are flat and thin, and re- 
volve on an axis nearly, if not exactly, coincident 
with the axis of their planet. Their stability, as we 
have seen, is guaranteed by conditions of wonderful 
complexity and delicacy, and the adjustment of the 
rings to the planet, (humanly speaking), would seem 
to be impossible after the formation of the planet. — 
At least it is beyond our power to conceive how this 
could be accomplished by any law of which we have 



THE COMETARY WORLDS. 249 

any knowledge, and we must refer their structure at 
once to the fiat of Omnipotence. 

Granting the formation of a single sun by the neb- 
ular theory, and we account at once for the formation 
of all other suns and systems throughout all space; 
and according to the advocates of this theory, the 
comets have their origin in masses of nebulous mat- 
ter occupying positions intermediate between two or 
more great centres, and held nearly in equilibrio, 
until, finally, the attraction of some one centre pre- 
dominates, and this uncondensed filmy mass com- 
mences slowly to descend towards its controlling orb. 
This theory would seem to be sustained, so far as a 
single truth can sustain any theory, by the fact that 
the comets come into our system from all possible di- 
rections, and pursue their courses around the sun 
either in accordance with, or opposed to, the direction 
in which the planets circulate. Their uncondensed 
or nebulous condition results from the feeble central 
attraction which must necessarily exist in bodies com- 
posed of such small quantities of matter. Moreover, 
in some cases at least, there is reason to believe, that 
in their perihelion passage they are entirely dissipa- 
ted into vapor by the power of the sun's heat, and 
may thus revolve for ages, going through alternate 
changes of solidification and evaporation. 

But whence come the enormous trains of light 
which sometimes attend these wandering bodies ? — 
The last return of Halley's comet has furnished the 
data for the positive illustration of this mysterious 
subject. Sir John Herschel, after a careful and most 
elaborate examination of all the physical character- 
istics of this comet, comes to the conclusion that the 



250 STRUCTURE OF THE UNIVERSE. 

figure of the comet, envelope and tail, could not be a 
figure of equilibrium under the law of gravitation. 
He is therefore compelled to bring in a repulsive force 
to explain the phenomena. 

I cannot do better than to quote his own language 
in this bold introduction of a new power. — " Nor let 
any one be startled at the assumption of such a re- 
pulsive force as here supposed. Let it be borne in 
mind that we are dealing (in the tails of comets) with 
phenomena utterly incompatible with our ordinary 
notions of gravitating matter. If they be material in 
that ordinary received sense which assigns to them 
only inertia and attractive gravitation, where, I would 
ask, is the force which can carry them round in the 
perihelion passage of the nucleus, in a direction point- 
ing continually from the sun, in the manner of a rigid 
rod, swept round by some strong directive power, and 
in contravention to all the laws of planetary motion, 
which would require a slower angular motion of the 
more remote particles, such as no attraction to the 
nucleus could give them, be it ever so intense ? The 
tail of the comet of 1680, in five days after its peri- 
helion passage, extended far beyond the earth's orbit 
having, in that brief interval, shifted its angular posi- 
tion nearly 150°. Where can we find, in its gravita- 
tion either to the sun, or to the nucleus, any cause for 
this extravagant sweep ? 

" But again, where are we to look (if only gravity 
be admitted) for any reasonable account of its pro- 
jection outward from the sun, putting its angular mo- 
tion out of the question ? Newton calculated that the 
matter composing its upper extremity quitted the nu- 



THE C0METARY WORLDS. 251 

cleus only two days previous to its arriving at this 
enormous distance." 

Herschel argues the inadequacy of gravitation to 
account for these wonderful phenomena. The velo- 
city with which the matter composing the tail shot 
forth from the head of the comet, from the sun, was 
far greater than that which the sun could impress on 
a body falling to it, even from an infinite distance. — 
An energy of a different kind from gravitation, and 
far more powerful, must exist, to produce such re- 
sults. If, then, we are forced to the admission that a 
power exists in the sun capable of repelling matter 
of a certain quality existing in comets, a way is 
opened for the explanation of some of the most diffi- 
cult problems with which the mind has been obliged 
to contend. 

The diminution of the periodic time of Encke's 
comet has led some astronomers to adopt the idea of 
the existence of a resisting medium. But in case the 
sun possesses the power of repelling the matter of 
comets in their perihelion passage, a part of the mat- 
ter thus repelled may be driven entirely beyond the 
attractive influence of the nucleus, and be irrecovera- 
bly lost. In this case, a diminution of mass would 
inevitably involve a like diminution of periodic time, 
a contraction of the orbit, and all the phenomena 
presented by this mysterious object. Herschel even 
thinks it possible, on this theory, to account for the 
separation of Biela's comet into two distinct objects, 
and it appears to me that it presents the most reason- 
able explanation of the luminous appearance seen at 
certain seasons of the year, called the zodiacal light. — 
This phenomenon appears to be a ring of nebulous 



252 STRUCTURE OF THE UNIVERSE. 

matter surrounding the sun, and some of whose par- 
ticles are sustained at a much greater distance than 
could be accounted for by gravitation. Admitting the 
repulsive power already adverted to, there is no diffi- 
culty in understanding how this nebulous ring may be 
sustained at a vast distance from the sun. 

Here we freely admit that we. enter the confines of 
the unknown. We have left the solid ground of truth 
and certainty, and are pushing our investigations into 
the dim twilight of the invisible and uncertain. But 
as antiquity predicted that the time would come when 
the comets would be traced in their career, their pe- 
riods revealed, and their orbits ascertained, so we may 
confidently hope that, at no very distant day, all the 
mysteries which hang around these chaotic worlds will 
be fully revealed, and a knowledge of their physical 
condition shall reward the long study and deep re- 
search of the human mind. 



LECTURE IX. 

THE SCALE ON WHICH THE UNIVERSE IS BUILT. 

Thus far our attention has been directed to an ex- 
amination of the achievements of the human mind 
within the limits of our own peculiar system. We 
have swept outward from the sun through the plane- 
tary worlds, until we have reached the frontier limits 
of this mighty family. Standing upon the latest found 
of all the planets, at a distance of more than 3,000,- 
000,000 of miles from the sun, we are able to look 
backwards, and examine the worlds and systems 
which are all embraced within the vast circumference 
of Neptune's orbit. An occasional comet, overleap- 
ing this mighty boundary, and flying swiftly past us, 
buries itself in the great abyss of space, to return 
after its " long journey of a thousand years," and re- 
port to the inhabitants of earth the influences which 
have swayed its movements in the invisible regions 
whither it speeds its flight. 

The magnificence and complexity of the great sys- 
tem of planets and satellites and comets which con- 
stitute the sun's retinue ; the immense magnitude of 
some of these globes ; their periods of revolution, and 
reciprocal action, would seem to furnish a sufficient 
exercise, not only for the highest intellectual efforts, 
but for the entire energy which the human mind can 
exert. But the whole of this stupendous scheme, as 

W '253) 



254 STRUCTURE OF THE UNIVERSE. 

we shall soon see, is but an infinitesimal portion of 
the universe of God, one unit among the unnumbered 
millions which fill the crowded regions of space. — 
Standing at the verge of the planetary system, we 
find ourselves surrounded by a multitude of shining 
orbs, some radiant with splendor, others faintly gleam- 
ing with beauty. The smallest telescopic aid suffices 
to increase their number in an incredible degree, 
while with the full power of the grand instruments 
now in use, the scenes presented in the starry heavens 
become actually so magnificent as to stun the imagi- 
nation and overwhelm the reason. Worlds and sys- 
tems, and schemes and clusters, and universes, rise in 
sublime perspective, fading away in the unfathomable 
regions of space, until even thought itself fails in its 
efforts to plunge across the gulf by which we are sepa- 
rated from these wonderful objects. 

In our measurements within the limits of the solar 
system, the radius of the earth's orbit has sufficed for 
a unit with w r hich to exhibit the distances of the plan- 
ets and comets. Great as is this unit, measuring no 
less than 95,000,000 of miles, we shall soon find it 
far too minute and insignificant to serve in our re- 
searches with reference to the grand scale of the visi- 
ble universe. To obtain comprehensible ideas with 
reference to the interstellar spaces, we shall be obliged 
to call to our aid a unit, not exactly of distance, but 
of velocity ; and before entering on the full exhibition 
of the main object of this lecture, permit me to direct 
your attention to a remarkable discovery, by which 
the important fact has been revealed, that light does 
not pass instantly from a luminous body to any re- 
mote object on which it may fall, but with a progres- 



SCALE ON WHICH THE UNIVERSE IS BUILT. 255 

sive motion, whose actual velocity has been ascer- 
tained. The important bearing of this discovery will 
become apparent as we advance in our examination 
of the sidereal heavens. 

After the motions of the four moons of Jupiter had 
been sufficiently observed to construct tables of their 
movements, with a view to predict their eclipses, 
some unaccountable phenomena presented them- 
selves, which, for a long time, baffled all efforts to 
explain them. It should be remembered, that the 
orbit of Jupiter encloses that of the earth, and when 
the two planets happen to be on the same side of the 
sun, and in a straight line passing through that orb, 
they are then at their least distance from each other, 
and are said to be in conjunction. Now suppose Ju- 
piter to remain stationary, at the end of half a year 
the earth will have reached the opposite point of her 
orbit, and will now be more distant from Jupiter by 
an amount equal to the diameter of her orbit, or 
nearly 200,000,000 of miles. Retaining carefully 
these positions in the mind, we shall follow the facts 
about to be presented with the greatest ease. 

It. was found that those eclipses of Jupiter's satel- 
lites, which occurred while the earth and planet were 
at their least distance from each other, always came 
on sooner than the time predicted by the tables ; while, 
on the contrary, those which took place when the 
planets were most remote from each other, occurred 
later than the computed time. A still more extended 
examination of these remarkable phenomena demon- 
strated the fact, that the discrepancies depended evi- 
dently on the absolute increase and decrease of dis- 
tance which marked the relative position of the plan- 



256 STRUCTURE OF THE UNIVERSE. 

ets in their revolutions around the sun. For a long 
time, no explanation of these undeniable truths could 
be found, until the mystery was finally solved by 
Roemer, a Danish astronomer, who, with admirable 
sagacity, traced these irregularities to their true 
source, and found that they arose from the fact that 
light traveled through space with a finite and meas- 
urable velocity. 

The explanation is simple. When Jupiter and the 
earth are at their least distance from each other, the 
stream of light flowing from the satellite of the great 
planet traverses a shorter space to reach the eye of 
the observer on the earth, by nearly 200,000,000 of 
miles, than when the planets are most remote from 
each other. In case, therefore, this stream is in any 
way cut off, it will run out sooner in the first than in 
the second position, by the time required to pass over 
the diameter of the earth's orbit. The stream of light 
is actually shorter, by 200,000,000 of miles, in the 
first than in the second position of the planets. 

Now the satellites of Jupiter receive their light 
from the sun ; — they reflect this light to the earth, and 
when the body of their primary is interposed between 
them and their source of light, they are eclipsed ; their 
light is cut off; its flow is interrupted ; and when the 
stream of light starting from them at the instant the 
supply is cut off shall have run out, then, and not till 
then, does the satellite become invisible. This ex- 
planation accounted for all the phenomena in the 
most beautiful manner. 

The tables had been constructed from the mean of 
a great number of observed eclipses. Hence, those 
which took place while Jupiter and the earth were 



SCALE ON WHICH THE UNIVERSE IS BUILT. 257 

near to each other, would happen earlier than pre- 
diction ; while those taking place when the planets 
were at their greatest distance, would occur later than 
the time given by the tables. But the velocity with 
which this mysterious, subtle, intangible substance 
called light, flew through the regions of space, as de- 
termined by this wonderful theory, was so great as to 
startle the minds of even its strongest advocates, and 
to demand the most positive testimony to induce the 
belief of those disposed to scepticism. It was found 
to traverse a distance equal to the entire diameter of 
the earth's orbit, or 190,000,000 of miles, in about 16 
minutes ! — giving a velocity of 12,000,000 of miles 
per minute, or 192,000 miles in each second of time ! 

It is not our purpose to enter into any investi- 
gation as to the true theory of light, whether it be an 
actual emanation from a luminous body of material 
particles, or whether it be a mere vibratory or undu- 
lating motion produced by luminous bodies on some 
ethereal medium. My only object, at this time, is to 
assert the undoubted fact, that in case a luminous 
body were to be suddenly called into being, and located 
in space at the distance of 12,000,000 of miles from 
the eye of an observer, who w r as on the look-out for 
its light, this light would not reach him until one minute 
after the creation of the object; and should it sud- 
denly be struck from existence, the same observer 
would behold it for one minute after the extinction. 

Should any mind revolt from these statements — 
should the difficulty of the investigation, and the in- 
credible velocity of light, demand higher and better 
evidence, before full faith can be given to the theory, 
I can only say that this evidence shall be given before 
w 2 



258 . STRUCTURE OF THE UNIVERSE. 

we close this discussion, and with a fullness and 
clearness which shall set all doubts at defiance. 

I now proceed to an examination of the great 
problem of the parallax of the fixed stars, a problem 
which has taxed the ingenuity of the greatest minds, 
and which has called into requisition the most admi- 
rable skill for a period of more than 300 years. A 
familiar explanation of the nature of this problem 
may prepare the way for a rapid sketch of the various 
means which have been employed in its solution. If 
it were possible to measure on the earth's surface a 
base line of a thousand miles in length, by locating 
an observer at each extremity of this base, with in- 
struments suitable to fix the moon's place among the 
fixed stars, the telescopes of those two observers, di- 
rected to the moon's centre at the same instant, would 
incline towards each other, and the visual ray from 
each of those instruments would meet at the moon's 
centre, and form an angle with each other. This an- 
gle, or opening of the visual rays, is called the parallax 
and in case the object under examination were a fixed 
star, then would the angle in question be called the 
parallax of the fixed star. 

It is readily seen that when the length of the base 
is known, and the parallactic angle measured, then 
the length of the visual ray may be at once deter- 
mined, and the distance of the object is made known 
by the simplest rules of geometry. Parallax, then, in 
general, is the apparent change in the place of an ob- 
ject, occasioned by the real change in the place of the 
spectator. 

The whirling of the trees of a forest, produced by 
the rapid speed of the beholder along a railway, is a 



SCALE ON WHICH THE UNIVERSE IS BUILT. 259 

parallactic motion, and becomes less and less percep- 
tible as the velocity of the spectator diminishes, or as 
the distance of the seemingly moving object becomes 
greater. To measure the distance of the fixed stars 
is then equivalent to determining the amount of par- 
allactic change in their relative positions, occasioned 
by the actual change of the positions from which they 
may be viewed by a spectator on the earth's surface. 

With the sun and moon and planets, a base line 
equal to the earth's diameter, or about 8,000 miles, 
has sufficed to produce a sensible and measurable 
parallax ;. but when we extend our visual rays to a 
fixed star, from the extremities of this base, their di- 
rections, to our senses, are absolutely parallel, or, in 
other language, the parallax arising from such a base 
is perfectly insensible. This first effort indicates, at 
once, the vast distance of the objects under examina- 
tion ; for such is the accuracy with which minute 
spaces are now divided, that parallax may be de- 
tected in case the object is even 160,000 times farther 
distant than the length of the base line. 

When the orbitual motion of the earth was first 
propounded by Copernicus, and it was asserted to 
revolve in an ellipse of nearly 600,000,000 of miles in 
circumference, and with a motion so swift that it 
passed over no less than 68,000 miles in every hour 
of time, the opponents of these startling doctrines ex- 
claimed No ! this is impossible ; for if we are sweep- 
ing around the sun in this vast orbit, and with this 
amazing velocity, then ought the fixed stars to whirl 
round each other, as do the forest trees to the trav- 
eler flying swiftly by them. 

But the stars of heaven do not move. Seen from 



260 STRUCTURE OF THE UNIVERSE. 

any point, and at any time, their places are ever the 
same, — fixed, immutable, eternal, — the bright and liv- 
ing witnesses of the extravagance and absurdity of 
this new and impossible theory. To this reasoning, 
which was well founded, and without sophistry, the 
Copernicans could only reply, that such was the enor- 
mous distance of the sphere of the fixed stars, that no 
perceptible change was occasioned by the revolution 
of the earth in its orbit. But this was mere assertion, 
and the opponents met the statement by this very 
plain exhibition of the case. — You who believe in the 
doctrines of Copernicus assert that the earth revolves 
on an axis, which, as it sweeps round the sun, re- 
mains ever parallel to itself. This axis prolonged 
meets the celestial sphere in a point called the north 
pole. Now as the earth describes an orbit of nearly 
200,000,000 of miles in diameter, its axis prolonged will 
cut out of the sphere of the heavens a curve of equal 
dimensions, and the pole will appear to revolve and 
successively fill every point of this celestial curve in 
the course of the year. Now the north pole does not 
revolve in any such curve ; it is ever fixed, and your 
theory is false. The Copernican could only reply 
that all the premises were true, but that the conclu- 
sion was false. The pole of the heavens did revolve 
in just such a curve as stated, but such was the dis 
tance of the sphere of the fixed stars, that this curve 
of 200,000,000 of miles in diameter was reduced to 
an invisible point ! 

Three hundred years have rolled away since this 
controversy began. The struggle has been long and 
arduous. The mind, baffled in one direction, has di- 
rected its energies in another — failing in one mode of 



SCALE ON WHICH THE UNIVERSE IS BUILT. 261 

research, it devises another, and thus struggling on- 
ward for three long centuries, it at length triumphs. 
The facts are developed, and the truth of the grand 
theory of Copernicus is vindicated and established, 
and the accuracy of these incredible statements is 
proved in the clearest manner. 

As this discussion exhibits, clearly and beautifully, 
the progressive advances of human genius, I shall 
be pardoned for entering, at some length, into an 
examination of the various attempts which have 
been made to resolve the problem of the parallax of 
the fixed stars. Indeed, the distance of the nearest 
fixed star is to become the unit of measure with which 
we are to traverse the innumerable worlds and sys- 
tems by which we are surrounded, and on the accu- 
racy with which it shall be determined will depend 
the correctness of the survey which we are soon to 
make. 

Failing entirely in obtaining any parallactic angle 
with a base line of 8,000 miles in length, the earth 
was employed to transport the observer from the first 
point of observation to a distance of 190,000,000 of 
miles, there again to erect his telescope, and to send 
up his second visual ray to the far distant star, in the 
hope of finding a parallactic angle with a base of 
such enormous extent. 

Permit me to illustrate the nature of this investi- 
gation. Suppose from the centre of a plane a solid 
granite rock, deep sunk and immoveable, rears its 
head far above the mists and impurities which float 
in the lower air. Ascending to the summit, the as- 
tronomer hews out some rough peak into the form of 
a vertical shaft. To this solid shaft he bolts the me- 



262 STRUCTURE OF THE UNIVERSE. 

tallic plates which shall bear his telescope. The in- 
strument is of a size and power commensurate with 
the grand objects which it is required to accomplish. 
Placed in a position such that its axis shall be exactly 
vertical, it is screw-bolted and iron-bound to the solid 
rock with fastenings which shall hold it from year to 
year, fixed and immoveable as its rocky base. 

To give more perfect precision to his work, the as- 
tronomer places in the focus of his eye-piece two 
delicate lines made from the spider's web, of a mi- 
nuteness almost mathematical, which, by crossing at 
right angles, form a point of the utmost precision ex- 
actly in the axis of the telescope. These are in like 
manner fixed immoveably in their places, and now 
the machinery is prepared with which the observa- 
tions are to be conducted. 

Suppose the observations to commence to-night. — 
■On placing the eye to the telescope, and looking di- 
rectly up to the zenith, a star enters the field of the 
instrument, and borne along by the diurnal motion of 
the heavens, advances towards the central point de- 
termined by the intersection of the spider's lines. In 
passing across the field of view, its minute diameter 
is exactly bisected by one of these delicate lines, and 
the exact moment, to the hundredth part of a second 
of time, is noted at which it passes the central point. 
This observation completed with all possible pre- 
cision, in case no change in the apparent place of the 
star is produced by the revolution of the earth in its 
orbit, or by any other cause, on each successive night 
throughout the entire year the same phenomena will 
be repeated in the same precise order. When the 
hour comes round, the star will enter the field, thread 



SCALE ON WHICH THE UNIVERSE IS BUILT. 263 

the spider's line, and reach the central point at the 
same precise instant, night after night, even for a 
thousand revolutions of the earth on its axis. 

Such, then, is the delicate means employed in the 
examination of the problem of the parallax of the 
fixed stars; and nearly in this way did Bradley, the 
great English astronomer, prosecute this intricate in- 
vestigation. If any change in the star's place is oc- 
casioned by the revolution of the earth in its orbit, 
sweeping, as it does, the spectator round the circum- 
ference of a track nearly 200,000,000 of miles in di- 
ameter, it is easy to compute, not the amount, but the 
direction in which these changes will be accomplished. 
These computations were made by the astronomer, 
and all things being prepared, he commenced the 
series of observations which were to lead to the most 
important results. The discovery of absolute fixity 
in the star would be a great negative result, and any 
changes, no matter of what kind or character, could 
not fail to be detected. 

Night after night was the astronomer found at his 
post, and as the months rolled slowly away, he began 
to perceive that his star, which, for a long time, 
threaded the spider's line as it was in the act of pass- 
ing the field of the telescope, began slowly to work 
off from this line, at last absolutely separating itself 
from it, and failing to reach the central point of the 
field at the precise instant first recorded. It soon be- 
came manifest that some cause or causes were oper- 
ating to produce an apparent change in the place of 
the star, but what was the astonishment of Bradley 
to find that trie changes in question could not be pro- 
duced by parallax, for the motions detected were al- 



264 STRUCTURE OF THE UNIVERSE. 

most precisely opposite to those which would arise 
from this cause. 

Long years of laborious examination were finally 
rewarded with two of the most brilliant discoveries 
ever accomplished by human skill and genius. The 
first of these demonstrated the fact that the sun and 
moon were so operating on the protuberant matter 
at the earth's equator as to cause the axis of the 
earth to oscillate or revolve in a minute orbit, nodding 
to and fro under the influence of the configurations 
of these two controlling bodies, and following, in the 
most absolute manner, their relative positions. The 
effect of this variation, called nutation, is to cause all 
the stars to appear alternately to approach and recede 
from the pole. — The real effect is to move the pole by 
the same amount. 

The value of this change has been determined with 
the utmost precision, and although its entire effect 
does not shift the pole over a greater space than the 
fourth part of the apparent diameter of the planet 
Jupiter, its values, as deduced by different astronomers, 
and by different processes, scarcely differ by the frac- 
tion of a second of space. As a specimen of the ac- 
curacy attained in these delicate measurements, I will 
give three values recently obtained by the Russian 
astronomers. — M. Busch, from Bradley's observations, 
obtains the value 9". 2320; M. Liendhal, from obser- 
vations at Derpat, finds the value 9". 1361 ; M. Peters, 
from right ascensions of Polaris, observed at Derpat, 
fixes the value at 9". 21 64. — The mean of the three 
values is 9". 2231, the highest difference from which is 
less than the tenth part of one second of arc. 

Valuable as was this discover}^ it was actually sur- 



SCALE ON WHICH THE UNIVERSE IS BUILT. 265 

passed by the importance of the second, for which we 
are in like manner indebted to Bradley. This second 
phenomenon consisted in an apparent movement of 
all the fixed stars in a minute orbit, which was ac- 
complished in a year for every individual, and showed, 
in the most absolute manner, that it depended in 
some way on the orbitual revolution of the earth. — 
For a long time, the true explanation of this phenom- 
enon, which Bradley saw at once was not parallactic, 
eluded his highest sagacity. Potent thought and per- 
severing reflection were, however, at last triumphant, 
and an explanation was finally reached, not only of 
the most satisfactory kind, but involving nothing less 
than an absolute demonstration of the orbitual mo- 
tion of the earth, and a full confirmation of the velo- 
city of light, whose prodigious swiftness had stag- 
gered the faith of many anxious to credit so marvel- 
ous a statement. 

A few words will suffice to explain these phenom- 
ena. If we admit the progressive motion of light and 
the revolution of the earth in its orbit, it is manifest 
that the celestial bodies will not occupy in the heavens 
the places they appear to fill. Take, for example, 
the planet Jupiter, and even suppose the planet to be 
fixed. The telescope is directed to this object, and 
the light from the planet, streaming through the axis 
of the instrument, reaches the eye of the observer, 
and produces the visible image of the planet. But 
these very particles of light have occupied nearly 40 
minutes in passing from the planet to the e}*e of the 
observer. During these 40 minutes, the earth has 
progressed in its orbit some 37,000 miles, and the 
spectator on the earth, borne along with it, must see 
X 



266 STRUCTURE OF THE UNIVERSE. 

the planet, not where it actually is, but where it was 
in appearance some forty minutes before. The same 
effect, in kind, is produced on the places of the fixed 
stars, and is called aberration. Understanding, now, 
that some effect must arise from these causes, (the ve- 
locity of light and the motion of the earth), let us 
endeavor to render its nature clear, and the results 
palpable. To accomplish this, we must resort to the 
simplest means of elucidation. 

Suppose a person were on the deck of a boat float- 
ing down the current of a river at any given rate per 
hour. As he moves steadily down the stream, he 
catches sight of an object on the shore, through which 
he proposes to send a rifle ball. The marksman will 
not aim directly at the object. Why? Because he 
knows that the rifle ball will partake of the boat's 
motion, and will be carried down, after it leaves the 
gun and before it reaches the mark, a distance equal 
to the progressive motion of the boat during the time 
of flight of the ball. To strike the mark, he must 
therefore make this necessary allowance, and aim 
above it the required quantity. It is readily seen that 
the faster the boat moves, the greater will this allow- 
ance be. 

Now reverse the proposition, and suppose a rifle 
fixed on shore, and so directed as to fire a ball down 
the barrel of a gun on a moving boat. In case the 
two rifles are on the same exact level, and the axes 
of the barrels come precisely to coincide, it might be 
supposed that if the fixed one is fired at the exact in- 
stant the muzzles come precisely opposite to each 
other, that the ball from the one will pass down the 
other. But this, from a moment's reflection, is found 



SCALE ON WHICH THE UNIVERSE IS BUILT. 267 

to be false. The fixed rifle must be fired before the 
moving one comes opposite, and the allowance must 
be made by knowing how long the ball requires to 
move from the one gun to the other, and with what 
velocity the moving piece is descending. This com- 
putation being accurately made, the ball from the 
shore might be made to enter the muzzle of the mov- 
ing rifle ; but while it is progressing down the barrel, 
the barrel itself is progressing down the stream, and 
hence, to avoid the pressure of the ball against the 
upper side of the barrel, we must fix it in an inclined 
position, and the bottom of the barrel must be as far 
up stream as it will descend by the boat's motion du- 
ring the progress of the ball down the barrel. Hence 
we see that the direction in which the barrel of the 
rifle which is to receive the ball is to be placed, is de- 
termined by the velocity of the ball, and the velocity 
of the boat which bears the rifle. 

Now for the application. The particles of light 
coming from the fixed stars are the balls from the 
fixed rifle. The boat corresponds to the earth sweep- 
ing around in its orbit, and bearing with it the tube 
of the astronomer, down whose axis the particles of 
light must pass to reach the observer's eye. The ve- 
locity of the earth's motion is well known, and the 
amount by which the telescope must be inclined, to 
cause the light to enter, has been accurately deter- 
mined, and from these two data the velocity of the 
light itself becomes known, and confirms, in the most 
satisfactory manner, the previously determined value 
of this incredible velocity, while the reality of the 
earth's motion is absolutely necessary to render the 
phenomena at all explicable. 



268 STRUCTURE OF THE UNIVERSE. 

Such were the beautiful results reached by Bradley, 
and although nothing was gained with reference to 
the parallax, these preliminary discoveries were in 
themselves of the highest value, and prepared the 
way for subsequent observers, who, with better 
means and more delicate instrumental aid, might 
prosecute the same great investigation. 

Amid the numerous and diversified researches of 
Sir William Herschel, the problem of the parallax of 
the fixed stars could not fail to engage his attention, 
by its difficulty and importance. He devised a new 
means of prosecuting this research, which seemed to 
promise the most certain success. In his exploration 
of the heavens with his powerful telescopes, he dis- 
covered the curious fact that many fixed stars which, 
to the unassisted eye, appear as single objects, under 
the space-annihilating power of the telescope, are 
seen to consist of two, sometimes of three or more, 
individual stars, so close to each other that, to the 
naked eye, they blend into a single object. 

Herschel, in the outset, conceived that this prox- 
imity of the stars was an accidental circumstance, 
and that where a pair could be found, in which one 
individual was about double the other in magnitude, 
it might reasonably be inferred that the smaller of the 
two was twice as deeply sunk in space as the larger. 
If this hypothesis could be shown to be true, then 
would these objects present an admirable means of 
detecting, with the greatest accuracy, any change in 
their relative positions, occasioned by the orbitual 
motion of the earth. In case their proximity was 
optical, or merely occasioned by the fact that the vis- 
ual ray drawn to the one passed nearly through the 



SCALE ON WHICH THE UNIVERSE IS BUILT. 269 

other, it is manifest that, shifting greatly the position 
of the observer, the stars might be made to open out 
or close up on each other, or even revolve the one 
about the other. In employing this mode of investi- 
gation, the objects of comparison fell within the field 
of view of the same telescope, and almost all extra- 
neous sources of error were eliminated. 

Such was the plan devised, or rather perfected by 
Herschel, (for his predecessors had already suggested 
it), and on the prosecution of which he entered with 
the zeal which ever distinguished this great astrono- 
mer. When he commenced his researches, some half 
dozen double stars had been discovered and recorded. 
His first duty was to increase this number as rapidly 
as possible, and from his entire catalogue to select 
those best adapted to his purpose. Under his pene- 
trating glance, the number of these curious duplex 
objects increased with astonishing rapidity, and he 
was himself startled with their frequent occurrence. 
However, with a mind fixed on his original design, he 
selected a large number of pairs, of such relative 
magnitudes, and in such positions, as promised 
the most certain success. Let it be remembered 
that many of these delicate objects were not divided 
from each other by a space greater than the thou- 
sandth part of the sun's diameter. 

To ascertain the apparent changes in the relative 
positions and distances of the stars composing these 
pairs, Herschel measured, with every care, the dis- 
tance which separated them, and took the direction 
of the line drawn from the centre of the one to the 
centre of the other. Variations of distance and po- 
sition, occasioned by parallax, were easily computed 
x 2 



270 STRUCTURE OF THE UNIVERSE. 

in kind and character, and the great astronomer com- 
menced and prosecuted his observations with san- 
guine hopes of success. One thing was certain: — all 
parallactic movements would have a period of one 
year, since they arise from the annual revolution of 
the earth in its orbit, and at the end of this period the 
stars composing the double sets ought to return to the 
position occupied at the outset. What was Herschel's 
astonishment to find that, in many instances, the stars 
composing these pairs were actually in motion ; but 
the movement was certainly not of a parallactic kind, 
for it neither agreed in direction or in period with the 
effects of parallax. Here was another grand discovery ! 
These double stars, which were scattered throughout 
the heavens with far greater profusion than accidental 
optical proximity could warrant, were found to be 
magnificent systems of revolving suns ! They were 
united by the law of gravitation, and exhibited the 
wonderful spectacle of stupendous globes, moving in 
obedience to the same influences which hold the plan- 
ets in their orbits, and guide the comets in their ec- 
centric career. — This is not the place to enter into de- 
tail concerning these wonderful objects. 

While a new field of investigation, boundless and 
magnificent, was opened up to the human mind ; 
while the great discoverer of these far-sweeping 
suns was more than rewarded for his toil and labor, 
the original object of his research was not only left 
un attained, but the method selected with so much 
reasonable hope of success, became utterly inapplica- 
ble. The parallactic and absolute motions of the 
systems of stars became so inextricably involved, that 



SCALE ON WHICH THE UNIVERSE IS BUILT. 271 

the imperfect micrometrical means of Herschel could 
not separate them. 

Thus far, the efforts to obtain the distance of the 
stars had been unavailing. — A negative solution had 
indeed been reached. That their distance was enor- 
mous, was made evident, from the fact that the par- 
allax had remained insensible, even under the most 
careful and delicate instrumental tests. Any absolute 
solution began almost to be despaired of, when hope 
was again revived by the magnificent refracting teles- 
copes, for which the world was indebted to the skill and 
genius of the celebrated Frauenhofer, of Munich. — 
This great artist, aided by the profound science of 
Bessel, contrived and executed an instrument of ex- 
traordinary power, and especially adapted to the re- 
search for the parallax of the fixed stars. 

Armed with a micrometrical apparatus of wonder- 
ful perfection, and capable of executing measures of 
great, as well as minute distances, the telescope was 
so arranged as to be carried forward by delicate ma- 
chinery, with a velocity exactly equal to the diurnal 
motion of the object under examination. — To give 
some idea of the delicacy of the contrivances with 
which these great telescopes have been provided, it 
is only necessary to state that the micrometer of the 
great Refractor of the Cincinnati observatory is capa- 
ble of dividing an inch into 80,000 equal parts ! — 
When mechanical ingenuity failed to construct lines 
of mathematical minuteness, the spider lent his aid, 
and it is with his delicate web that these measures 
are accomplished. Two parallel spider's webs are 
adjusted in the focus of the eye-piece of the microme- 
ter, and when the light of a small lamp is thrown 



272 STRUCTURE OF THE UNIVERSE. 

upon them, the eye, on looking through the telescope, 
sees two minute golden wires, straight and beautiful, 
drawn across the centre of the field of view, and pic- 
tured on the heavens. These are within the control 
of the observer. He can increase or decrease their 
distance at pleasure, and so revolve them as to bring 
them into any position, every motion being accurately 
measured by properly divided scales. 

Suppose, then, it is desired to take the distance and 
position of the stars forming a pair. The telescope 
is directed to them, and they are brought to the centre 
of the field of view. The clock work is set in action ; 
it takes up the ponderous instrument, weighing more 
than 2,500 pounds, and with the most astonishing 
accuracy it bears it onward, keeping its mighty eye 
fixed on the object under examination. The observer 
is thus left with both hands free to make his meas- 
ures. — He first revolves his micrometer spider's lines 
round until one of them shall exactly pass from centre 
to centre of the two stars. This position is noted, 
and from it is deduced the angle formed by this line 
with the meridian. He then revolves them a quarter 
of the circumference, and they are then perpendicular 
to their former position. He now separates the wires 
until the one shall exactly bisect one star, while the 
other wire passes through the centre of the second 
star, reading this distance on the proper scale. He 
has fixed, in these two observations, the position and 
distance of the two components of the double set. — 
Such is the precision attained in this work, that the 
most minute motions cannot escape detection. If the 
stars separate from each other at so slow a rate that 
a million of years would be required to perform the 



SCALE ON WHICH THE UNIVERSE IS BUILT. 273 

circuit of the heavens, their motion would be detected 
in half a year ! 

With machinery more delicate even than this, and 
better adapted to the purpose, and of a kind some- 
what different, Bessel once more renewed the re- 
search after the unattainable parallax of the fixed 
stars. His great instrument, called the heliometer, was 
mounted as early as 1829, but a multitude of causes, 
and some unsuccessful efforts, delayed his principal 
operations up to August, 1837. Three great princi- 
ples guided him in his selection of 61 in the Swan, 
as the star on which to perform his observations. — 
First. It was affected by a very great proper motion, a 
characteristic which we will explain fully hereafter, 
and which indicated it to be among the nearest of all 
the stars. Second. Its duplex character adapted it 
especially to the instrument he was about to employ. 
Third. The region occupied by 61 Cygni contains a 
number of minute stellar points, close to the double 
star, and presenting admirable fixed points, to which 
the relative motions of the two components of the 
star to be measured might be referred. 

With these advantages, and a magnificent instru- 
ment, Bessel commenced his observations. He meas- 
ured the distance from the centre of the line joining 
the two stars, to two of the small stellar points, which 
served him as points of reference, and this kind of 
observation was repeated night after night, whenever 
the stars were visible, from the middle of August, 1837, 
up to the end of September, 1838. The entire series 
of observations was then taken and corrected for 
every possible known error, and in case any appre- 



274 STRUCTURE OF THE UNIVERSE. 

ciable change remained, it could only be attributed to 
parallax. 

After a most careful and elaborate investigation, a 
variation commenced to show itself, increasing pre- 
cisely as parallactic variation ought to increase, and 
diminishing as it ought to diminish. The period of 
these changes was precisely a year, and in all partic- 
ulars, there was an exact correspondence in kind 
with the changes which ought to be produced by par- 
allax. But such was their minute character, that 
Bessel hesitated. 

During another year the observations were repeated. 
The same results came out, and the previous values 
were confirmed. A third year's observations, yield- 
ing precisely the same values, removed all doubt, and 
the great Koeningsburgh philosopher announced to 
the world that he had passed the impassable gulf of 
space, and had measured the distance to the sphere 
of the fixed stars ! But how shall I convey any ade- 
quate idea of this stupendous distance ? Millions 
and millions of miles serve only to confound the 
mind. Let us employ a different kind of unit. 

Light, as we have seen, travels with a velocity of 
12,000,000 of miles in every minute of time. Hence, 
to reach us from the most remote of all the planets, 
Neptune, whose distance from the sun is about 3,000,- 
000,000 of miles, will require a journey of about four 
hours ; but to wing its flight across the interval which 
separates our sun from 61 Cygni, will require a pe- 
riod not to be reckoned by hours, or by days, or by 
months. Nearly ten years of time must roll away 
before its light, flying, in every second, 192,000 miles, 
can complete its mighty journey ! If the mind re- 



SCALE ON WHICH THE UNIVERSE IS BUILT. 275 

volts at this conclusion ; if the distance be too great 
for comprehension ; if the scale of the universe thus 
suggested even staggers the imagination, I can only 
say, that all subsequent observation has confirmed, in 
the most satisfactory manner, the accuracy of Bessel's 
results. This great astronomer first led the way 
across the mighty gulf which separates us from the 
fixed stars. The distance once passed, the route has 
become comparatively easy, and succeeding observers 
have determined the parallax of a sufficient number 
of stars to show that their results are entirely trust- 
worthy. 

Having now succeeded in gaining a knowledge of 
the distance which separates our sun from its remote 
companions, we are prepared to extend our explora- 
tions of the universe. The question naturally arises, 
how are the stars distributed throughout space ? — are 
they indifferently scattered in all directions, or are 
they grouped together into magnificent systems ? A 
cursor}^ examination of the starry heavens with the 
naked eye shows us, that so far as the larger stars 
are concerned, they do not appear to have been dis- 
tributed in the celestial sphere according to any deter- 
minate law; but on applying the telescope, that lu- 
minous zone which, under the name of the Milky Way, 
girdles the whole heavens, is found to be composed of 
minute stars, scattered like millions of diamond points 
on the deep blue ground of the sky. 

Sir William Herschel conceived the idea that it 
might be possible to fathom this mighty ocean of 
stars, and to determine its metes and bounds; to give 
to it figure, and to circumscribe its limits. It will not 
be difficult to explain, in a few words, the general 



276 STRUCTURE OF THE UNIVERSE. 

outline of the plan adopted by this extraordinary man 
in the prosecution of this wonderful undertaking. — 
In case we admit that the stars are of equal magni- 
tudes, and at equal distances from each other, it 
would not be difficult to ascertain how far they ex- 
tended in any given direction, the one behind the 
other. It is manifest, that in examining the heavens 
with a telescope of given power and aperture, we 
shall be able to count more stars in the field of view 
in those regions where they are so arranged as to 
reach farthest back into space; and in case we know 
their absolute distance from each other, the number 
counted in any field of view, will determine with cer- 
tainty the length of the visual ray reaching to the 
most remote star visible in that field. 

Now, although the hypothesis that the stars are 
of equal magnitude, and are uniformly distributed 
through space, may not be rigorously true, yet doubt- 
less the mean distances are not far from this hypothe- 
sis ; and although our results may only be approxi- 
mate, yet as such they are to be relied upon, and they 
become the more interesting as they carry us to the 
utmost limits of human investigation. Armed with 
his mighty telescopes, Sir William Herschel com- 
menced the stupendous task of sounding the heavens, 
with the purpose of ascertaining whether the stars 
composing the Milky Way were unfathomable, or 
were bounded and circumscribed by definite limits. 

Sweeping a circle round the heavens which cut this 
grand stratum of stars in a direction nearly perpen- 
dicular to its circumference, he directed his great tel- 
escope to a certain number of points along this circle, 
and as he moved slowly onward, counted all the stars 



SCALE ON WHICH THE UNIVERSE IS BUILT. 277 

visible in each field of view. It was fair to conclude, 
that wherever most stars were to be seen, there was 
the stratum deepest. Having gone entirely around 
the heavens, along the circumference of his circle, he 
had sounded the depth of the stars along a section 
of the Milky Way, and to obtain the figure of the sec- 
tion thus cut out was not a difficult matter. 

He assumed a central point on paper to represent 
his point of observation. He then drew from this 
point lines radiating, and in the actual directions 
which he had given to his telescope while engaged in 
his explorations. On each of these indefinite lines 
he laid off a distance proportioned to the number of 
stars counted in the field of view in the direction 
which the line represented, and by joining these 
points thus determined, he formed a figure which rep- 
resented the relative depths to which he had pene- 
trated into space ; and in case he could be certain 
that he had gone absolutely through the stratum in 
every instance, and had grasped every star, even 
where the extent was most profound, the figure thus 
constructed would represent the form of the line cut 
from the outside boundary of the Milky Way by the 
plane of the circle in which the explorations had been 
made. 

Did he then actually penetrate the deepest por- 
tions, or any portion, of the Milky Way ? This was 
now his grand question, and to its decision he gave 
all his power and ingenuity. As a unit wherewith 
to measure the space-penetrating power of his teles- 
copes, he assumed the power of the human eye, and 
knowing that stars of the sixth magnitude are within 
the reach of the unaided eye, he concluded, from the 



Y 



278 STRUCTURE OF THE UNLVERSE. 

law regulating the decrease of light, that these mi- 
nute stars were twelve times more distant than the 
nearest or brightest stars. Now a telescope having 
an aperture such as to concentrate twice as much 
light as the eye, would penetrate into space twice as 
far, or would reach stars of the twenty-fourth order 
of distances, and so on for telescopes of all sizes. — 
In this way he concluded that his great forty foot re- 
flector, with a diameter of four feet, would penetrate 
194 times as far as the naked eye, or that it would 
still see a star of the first magnitude if it were car- 
ried backward into space 2,328 times its present 
distance ! 

Such, then, was the computed length of the sound- 
ing line employed in gauging these mighty depths. — 
Suppose, then, it was required to determine whether 
this line actually penetrated any given region of the 
Milky Way. Even with a single telescope, a series 
of experiments may be performed which go very far 
to determine this great question. As the space-pene- 
trating power of a telescope depends on the diameter 
of its aperture, it is easy to give to the same instru- 
ment different powers, by covering up, by circular 
coverings, certain portions of its object glass. Take 
circles of paste-board, or any other suitable material, 
and in the first cut an opening one inch in diameter, 
in the second an opening of two inches, and so on, 
up to the diameter of the object glass. These dia- 
phragms being successively applied to the object 
glass, give to the telescope space-penetrating powers 
proportioned to the diameter of the openings. 

In this way Herschel prepared himself to explore 
one of the deepest portions of the Milky Way. The 



SCALE ON WHICH THE UNIVERSE IS BUILT. 279 

spot selected was a nebulous or hazy cloud in the 
sword handle of Perseus, in which, to the naked eye, 
not a solitary star was visible. I have many times 
examined the same object, which is certainly one of 
the most magnificent the eye ever beheld. With the 
lowest telescopic aid, many stars are rendered visible, 
surrounded by a hazy light, in which minute glimpse 
points are occasionally to be seen. As the space- 
penetrating power was increased, the bright spots of 
light were successively resolved into groups of bril- 
liant stars, and more nebulous haze came up from the 
deep distance, indicating that the visual ray was not 
long enough to fathom the mighty distance. At last 
the full power of his grand instrument was brought 
to bear, when a countless multitude of magnificent 
orbs burst on the sight, like so many sparkling dia- 
monds on the deep blue of the heavens. There was 
no haze behind ; the telescopic ray had shot entirely 
through the mighty distance, and the clear deep hea- 
vens formed the back- ground of the brilliant picture. 
Thus did Herschel penetrate to the limits of the 
Milky Way, and send his almost illimitable sounding 
line far beyond, into the vast abyss of space, bound- 
less and unfathomable. And now do you inquire the 
depth of this stupendous stratum of stars ? The an- 
swer may be given, since we have the unit of measure 
in the distance of stars of the first magnitude. Light, 
with its amazing velocity, requires ten years to come 
to us from the nearest fixed stars, and yet Sir Wil- 
liam Herschel concluded, from the examinations he 
had been able to make, that in some places the depth 
of the Milky Way was such, that no less than 500 
stars were ranged one behind the other in a line, each 



280 STRUCTURE OF THE UNIVERSE. 

separated from the other by a distance equal to that 
which divides our sun from the nearest fixed star. — 
So that, for light to sweep across the diameter of this 
vast congeries of stars, would require a period of a 
thousand years at the rate of 12,000,000 of miles in 
every minute of time ! 

The countless millions of stars composing the 
Milky Way appear to be arranged in the form of a 
flat zone or ring, or rather stratum, of irregular shape, 
which I shall explain more fully hereafter. Its extent 
is so great as properly to form a universe of itself. — 
If it were possible, to-night, to wing our flight to any 
one of the bright stars which blaze around us, sweep- 
ing away from our own system, until planet after 
planet fades in the distance, and finally the sun itself 
shrinks into a mere star, alighting on a strange 
world that circles round a new and magnificent sun, 
which has grown and expanded in our sight, until it 
blazes with a magnificence equal to that of our own, 
here let us pause and look out upon the starry hea- 
vens which now surround us. 

We have passed over sixty millions of millions of 
miles. We have reached a new system of worlds re- 
volving about another sun, and from this remote 
point we have a right to expect a new heavens, as 
well as a new earth on which we stand. But no. — 
Lift up your eyes, and lo ! the old familiar constella- 
tions are all there. Yonder blazes Orion, with its 
rich and gorgeous belt ; there comes Arcturus, and 
yonder the Northern Bear circles his ceaseless journey 
round the pole. All is unchanged, and the mighty 
distance over which we have passed is but the thou- 
sandth part of the entire diameter of this grand clus- 



SCALE ON WHICH THE UNIVERSE IS BUILT. 281 

ter of suns and systems ; and although we have 
swept from our sun to the nearest fixed star, and 
have traveled a distance which light itself cannot 
traverse in less than ten years, yet the change 
wrought by this mighty journey, in the appearance 
of the heavens, is no greater than would be produced 
in the relative positions of the persons composing 
this audience to a person near its centre, who should 
change his seat with his immediate neighbor ! 

Such, then, is the scale on which the starry heavens 
are built. If, in examining the magnificent orbits of 
the remoter planets, and in tracing the interminable 
career of some of the far-sweeping comets, we feared 
there might not be room for the accomplishment of 
their vast orbits, our fears are now at an end. There 
is no jostling here; there is no interference, no per- 
turbation of the planets of one system by the suns of 
another. Each is isolated and independent, filling 
the region of space assigned, and within its own 
limits, holding on its appointed movements. 

Thus far we have spoken only of the Milky Way. 
In case it be possible to pierce its boundaries, and 
pass through into the regions of space which lie be- 
yond, the inquiry arises, what meets the vision there? 
What lies beyond these mighty limits ? Does crea- 
tion cease with this one great cluster, and is all blank 
beyond its boundary? 

Here again the telescope has given us ah answer. 
When we shall have traveled outward from our own 
sun, and passed in a straight line from star to star, 
until we shall have left behind us in grand perspec- 
tive a series of five hundred suns, we then stand on 
the confines of our own great cluster of stars. All 
y2 



282 STRUCTURE OF THE UNIVERSE. 

behind blazes with the light of countless orbs, scat- 
tered in wild magnificence, while all before us is deep, 
impenetrable, unbroken darkness. No glance of hu- 
man vision can pierce the dark profound. 

But summoning the telescope to our aid, let us par- 
sue our mighty journey through space ; far in the dis- 
tance we are just able to discover a faint haze of light 
— a minute luminous cloud which comes up to meet 
us — and towards this object we will urge our flight. 
We leave the shining millions of our own great clus- 
ter far behind. Its stars are shrinking and fading ; 
its dimensions are contracting. It once filled the 
whole heavens, and now its myriads of blazing orbs 
could almost be grasped with a single hand. But 
now look forward. — A new universe, of astonishing 
grandeur, bursts on the sight. The cloud of light has 
swelled and expanded, and its millions of suns now 
fill the whole heavens. 

We have reached the clustering of ten millions of 
stars. Look to the right ; there is no limit ; — look to 
the left ; there is no end. Above, below, sun rises 
upon sun, and system on system, in endless and im- 
measurable perspective. Here is a new universe, as 
magnificent, as glorious as our own, — a new Milky 
Way, whose vast diameter the flashing light would 
not cross in a thousand years. Nor is this a solitary 
object. Go out on a clear cold winter night, and 
reckon the stars which strew the heavens, and count 
their number, and for every single orb thus visible to 
the naked eye the telescope reveals a universe, far 
sunk in the depths of space, and scattered with vast 
profusion over the entire surface of the heavens. 

Some of these blaze with countless stars, while 



SCALE ON WHICH THE UNIVERSE IS BUILT. 283 

others occupying the confines of visible space, but 
dimly stain the blue of the sky, just perceptible with 
the most powerful means that man can summon to 
the aid of his vision. These objects are called clus- 
ters and nebulae, — clusters when near enough to per- 
mit their individual stars to be shown by the telescope, 
nebulae when the mingled light of all their suns and 
systems can only be seen as a hazy cloud. 

Thus have we risen in the orders of creation. We 
commenced with a planet and its satellite ; — we rose 
to the sun and its revolving planets, a magnificent 
system of orbs, all united into one great family, and 
governed by the same great law ; and we now find 
millions of these suns clustered and associated to- 
gether in the formation of distinct universes, whose 
number, already revealed to the eye of man, is not to 
be counted by scores or hundreds, but has risen to 
thousands, while every increase of telescopic power 
is adding by hundreds to their catalogue. 

Let us now explain these " island universes," as 
the Germans have aptly termed them, and attempt 
approximately to circumscribe their limits, and meas- 
ure their distances from us, and from each other. — 
Sir William Herschel, to whom we are indebted for 
this department of astronomy, conceived a plan by 
which it was possible approximately to sound the 
depths of space, and determine, within certain limits, 
the distance and magnitudes of the clusters and neb- 
ulae within the reach of his telescopes. To convey 
some idea of his method of conducting these most 
wonderful researches, imagine a level plane, of in- 
definite extent, and along a straight line, separated 
by intervals of one mile each, let posts be placed, 



284 STRUCTURE OF THE UNIVERSE. 

bearing boards on which certain words are printed in 
letters of the same size. The words printed on the 
nearest board, we will suppose, can just be read with 
the naked eye. To read those on the second, teles- 
copic aid is required, and that power which suffices to 
enable the letters to be distinctly seen, is exactly 
double that of the unaided eye. The telescope reveal- 
ing the letters at the distance of three miles is three- 
fold more powerful than the e}^e, and so of all the 
others. In this way we can provide ourselves with in- 
struments whose space-penetrating power, compared 
with that of the eye, can be readily obtained. 

Now to apply these principles to the sounding of 
the heavens. The eye, without assistance, would 
follow and still perceive the bright star Sirius, if re- 
moved back to twelve times its present distance. — 
After this, as it recedes, it must be followed by the 
telescope. Suppose, then, a nebula is discovered 
with a telescope of low power, and it is required to 
determine its character and distance. The astrono- 
mer applies one power after another, until he finally 
employs a telescope of sufficient reach to reveal the 
separate stars of which the object is composed, which 
shows it to be a cluster ; and since the space-pene- 
trating power of this instrument is known, relative to 
that of the human eye, in case the power is one hun- 
dred times greater than that of the eye, then would 
the cluster be located in space one hundred times far- 
ther than the eye can reach, or twelve hundred times 
more remote than Sirius, or at such a distance that 
its light would only reach our earth after a journey 
of 120,000 years ! 

Such was Herschel's method of locating these ob- 



SCALE ON WHICH THE UNIVERSE IS BUILT. 285 

jects in space. Some are so remote as to be far be- 
yond the reach of the most powerful instruments, and 
no telescopic aid can show them other than nebulous 
clouds of greater or less extent. It was while pursu- 
ing these grand investigations that Herschel was led 
to the conclusion, that among the nebulae which were 
visible in the heavens, there w r ere some composed of 
chaotic matter, a haz} r , luminous fluid, like that occa- 
sionally thrown out from comets on their approach to 
the sun. 

Among these chaotic masses he discovered some in 
which the evidences of condensation appeared mani- 
fest, while in others he found a circular disc of light, 
with a bright nucleus in the centre. Proceeding yet 
farther, he found well formed stars surrounded by a 
misty halo, which presented all the characteristics of 
what he now conceived to be nebulous fluid. Some 
of the unformed nebulae were of enormous extent, 
and among those partially condensed, such as the 
nebulae with planetary discs, many were found so 
vast that their magnitude would fill the space occu- 
pied by the sun and all its planets, forming a sphere 
with a diameter of more than 6000 millions of miles. 
Uniting these and many other facts, the great astron- 
omer was finally brought to believe, that worlds and 
systems of worlds might yet be in the process of for- 
mation, by the gradual condensation of this nebulous 
fluid, and that from this chaotic matter originally 
came the sun and all the fixed stars which crowd the 
heavens. This theory, extended, but not modified, in 
the hands of Laplace, is made to account for nearly 
all the phenomena of the solar system, and has been 
already referred to in a former lecture. 



286 STRUCTURE OF THE UNIVERSE. 

For a long time, this bold and sublime speculation 
was looked upon, even by the wisest philosophers, 
with remarkable favor. The resolution of one or two 
nebulae, (so classed by Herschel), with the fifty-two 
feet reflector of Lord Rosse, has induced some persons 
to abandon the theory, and to attempt to prove its 
utter impossibility. All that I have to say, is, that 
Herschel only adopted the theory after he had resolv- 
ed many hundreds of nebulae into stars ; and if there 
ever existed a reason for accepting the truth of this 
remarkable speculation, that reason has been scarcely 
in any degree affected by recent discoveries. 

I have examined a large number of these mysteri- 
ous objects, floating on the deep ocean of space like 
the faintest filmy clouds of light. No power, how- 
ever great, of the telescope, can accomplish the slight- 
est change in their appearance. So distant that their 
light employs (in case they be clusters) hundreds of 
thousands of years in reaching the eye that gazes 
upon them, and so extensive, even when viewed from 
such a distance, as to fill the entire field of view of 
the telescope many times. Sirius, the brightest, and 
probably the largest of all the fixed stars, with a di- 
ameter of more than a million of miles, and a dis- 
tance of only a single unit, compared with the tens of 
thousands which divide us from some of the nebulae ; 
and yet this vast globe, at this comparatively short 
distance, is an inappreciable point in the field of the 
telescope. What, then, must be the dimensions of 
those objects, which, at so vast a distance, fill the en- 
tire field of view even many times repeated ? 

Herschel computes that the power of his great re- 
flector would follow one of the large clusters if it 



SCALE ON WHICH THE UNIVERSE IS BUILT. 287 

were plunged so deep in space that its light would re- 
quire 350,000 years to reach us, and the great teles- 
cope of Lord Rosse would pursue the same object 
probably to ten times this enormous distance. 

Such examinations absolutely overwhelm the mind, 
and the wild dream of the German poet becomes a 
sort of dreadful sublime reality : — 

" God called up from dreams a man into the vesti- 
bule of heaven, saying, ' Come thou hither, and see 
the glory of my house.' And to the servants that 
stood around his throne he said, ' Take him, and un- 
dress him from his robes of flesh : cleanse his vision, 
and put a new breath into his nostrils : only touch 
not with any change his human heart — the heart 
that weeps and trembles.' It was done : and, with a 
mighty angel for his guide, the man stood ready for 
his infinite voyage ; and from the terraces of heaven, 
without sound or farewell, at once they wheeled away 
into endless space. Sometimes with the solemn flight 
of angel wing they fled through Zaarrahs of darkness, 
through wildernesses of death, that divided the worlds 
of life ; sometimes they swept over frontiers, that 
were quickening under prophetic motions from God. 
Then, from a distance that is counted only in heaven, 
light dawned for a time through a sleepy film ; by un- 
utterable pace the light swept to them, they by unut- 
terable pace to the light. In a moment the rushing 
of planets was upon them : in a moment the blazing 
of suns was around them. 

" Then came eternities of twilight, that revealed, 
but were not revealed. On the right hand and on the 
left towered mighty constellations, that by self-repeti- 
tions and answers from afar, that by counter-positions, 



288 STRUCTURE OF THE UNIVERSE. 

built up triumphal gates, whose architraves, wh se 
arch-ways— horizontal, upright — rested, rose — at alti- 
tude by spans — that seemed ghostly from infinitude. 
Without measure were the architraves, past number 
were the archways, beyond memory the gates. Within 
were stairs that scaled the eternities below ; above 
was below — below was above, to the man stripped 
of gravitating body : depth was swallowed up in 
height insurmountable, height was swallowed up in 
depth unfathomable. Suddenly, as thus they rode 
from infinite to infinite, suddenly, as thus they tilted 
over abysmal worlds, a mighty cry arose — that sys- 
tems more mysterious, that worlds more billowy, — 
other heights and other depths, — were coming, were 
nearing, were at hand. 

" Then the man sighed, and stopped, shuddered, and 
wept. His overladened heart uttered itself in tears ; 
and he said — 'Angel, I will go no farther. For the 
spirit of man acheth with this infinity. Insufferable 
is the glory of God. Let me lie down in the grave 
and hide me from the persecution of the infinite; for 
end, I see, there is none.' And from all the listening 
stars that shone around issued a choral voice, ' The 
man speaks truly : end there is none, that ever yet 
we heard of.' 'End is there none?' the angel 
solemnly demanded : ' Is there indeed no end ? — and 
is this the sorrow that kills you ? ' But no voice an- 
swered, that he might answer himself. Then the 
angel threw up his glorious hands to the heaven of 
heavens, saying, 'End is there none to the universe 
of God. Lo! also there is no beginning.' " 



LECTURE X. 

THE MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 

Having reached, in the course of the preceding lec- 
ture, to the outermost confines of the visible creation, 
let us now return home from this survey of the " island 
universes " which crowd the illimitable regions of 
space, to the stars which compose our own cluster, 
and learn how far the human mind has progressed in 
its examination of the millions of suns which consti- 
tute, in a more definite sense, our own Milky Way. 

We have already seen that the parallax of 61 
Cygni rewarded the laborious and extraordinary ef- 
forts of Bessel. The example set by this great as- 
tronomer encouraged those who followed him, and 
while his results in this particular case have been 
confirmed in the most astonishing manner, the dis- 
tances of many other stars have been obtained, until 
a sufficient amount of data has been accumulated to 
determine the approximate distances of the spheres 
of the fixed stars of different magnitudes. Struve es- 
timates the mean distance of stars of the first magni- 
tude to be 986,000 times the radius of the earth's 
orbit, or so remote that their light reaches us only 
after a journey of fifteen years and a half. Stars of 
the second magnitude send us their light in twenty- 
eight years, those of the third magnitude in forty- 
three years ; while the light from stars of the ninth 

Z ' 289 ) 



290 



STRUCTURE OF THE UNIVERSE. 



magnitude only reaches the eye of the observer after 
traversing 3pace for five hundred and eighty-six years, 
at the rate of twelve millions of miles in every min- 
ute of time. 

My range of investigation does not permit me to 
explain, at this time, how these extraordinary conclu- 
sions have been reached. The reasoning, however, is 
close and clear, and the results are no doubt approxi- 
mately correct. 

Such, then, are the distances separating man from 
the objects of his research. To have attained to a 
knowledge of these distances even, is sufficiently 
wonderful, but what we are about to reveal as the 
results of human investigation among these far dis- 
tant orbs, cannot fail to fill the mind with astonish- 
ment, and demonstrate the great truth that " man has 
been made but a little lower than the angels." 

Before it became possible to examine with absolute 
certainty the places of the stars, with a view to as- 
certain their absolute fixity, many difficult preliminary 
preparations had to be accomplished. Instruments 
of the most perfect kind must be provided, not only 
in their optical performances, but in their space-di- 
viding machinery. Moreover, the places of the stars, 
as determined by the best telescopes, must be cor- 
rected for every possible instrumental error. The 
two points to which the stars are referred are the 
north pole and the vernal equinox. In case any mo- 
tions belong to these points, their amounts and di- 
rections must be ascertained and allowed for. Then 
the effects of refraction, and of the abberration of 
light, were indispensable to a perfect investigation of 
the absolute places of the stars. 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 291 

All these and many other preliminary matters hav- 
ing been satisfactorily determined, it became possible 
to examine, in the most critical manner, the places of 
the stars, and to learn whether indeed, (as had been 
supposed for thousands of years), their configura- 
tions were eternal and unchangeable, or whether they 
moved among themselves with a motion rendered so 
slow by their immense distance, as hitherto to have 
escaped the most scrutinizing watch. 

Fully armed with the necessary instruments, it did 
not require many years to determine the grand truth, 
that among the tens of thousands of stars which fill 
the heavens, not a solitary one, in all probability, is 
in a state of absolute rest. Man}^ were found to 
move so swiftly, that their velocity was determined 
even in a single year; while others, in consequence of 
their enormous distance, may require centuries to de- 
tect any appreciable change. In the outset these ex- 
traordinary movements seemed to be directed by no 
law — some stars were sweeping in one direction, and 
some in another. Motion, ceaseless, eternal motion, 
seems to be stamped on the entire universe, and 
while the stars are pursuing their mighty orbits, we 
cannot resist the idea that our own sun, the centre of 
our great planetary system, itself a star, must partici- 
pate in the general movement, and is, in all probabil- 
ity, urging its flight, accompanied by all its planets, 
satellites, and comets, to some unknown region of 
space. 

The revolution of the stars, the organization of the 
grand cluster with which our sun is associated, the 
demonstration of the sun's absolute translation through 
space, its direction, velocity, and period, are the topics 



292 STRUCTURE OF THE UNIVERSE. 

to which I invite your attention in the closing lecture 
of the present course. 

When forced to acknowledge the rotation of our 
globe on its axis, and its swift orbitual motion, sur- 
rounded by wheeling planets and flying comets, the 
mind naturally retreats to the sun as the great im- 
moveable centre, where it can rest and contemplate 
these circling worlds. But even here, as we shall 
presently see, there is no rest. The sun himself be- 
comes a subordinate member of a grander combina- 
tion of worlds, and, obedient to higher influence, 
sweeps around in its unmeasured orbit. 

We shall present a rapid summary of the evidences 
of change among the fixed stars, and then proceed to 
develop the reasoning by which the direction and 
velocity of the sun's motion in space has been 
determined. 

More than two thousand years ago, the celebrated 
Greek astronomer, Hipparchus, was astonished by 
the sudden bursting forth of a brilliant star in a re- 
gion of the heavens where none had previously ex- 
isted. Up to this time, no doubt of the immutability 
of the starry sphere seems to have been entertained, 
and while the philosopher gazed and wondered, he 
resolved to execute a work from w 7 hich posterity 
might learn the changes of the celestial sphere. He 
undertook and completed his great catalogue of the 
places of a thousand stars, locating them with all the 
accuracy permitted by the rude instruments then in 
use. Subsequent observers, by comparing their own 
determined positions of the stars with their places as 
fixed on the catalogue of Hipparchus, could readily 
perceive any sensible change which might occur in 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 293 

their configuration, the appearance of new stars, or 
the disappearance of those which had once existed. 

The sudden breaking forth of a new star is a phe- 
nomenon of such wonderful character that we might 
well doubt the possibility of its occurrence, if we 
were obliged to rely on the historical account trans- 
mitted to us from the time of Hipparchus. But, for- 
tunately, more than one brilliant example of the kind 
has occurred in modern times, presenting the most 
unequivocal evidence of the reality of this inexpli- 
cable wonder. 

In 1572, a new star of great splendor appeared 
suddenly in the constellation Cassiopeia, occupying 
a position which had previously been blank. This 
star was first perceived by Schuler, of Wittemburg, 
on the 6th of August. It was detected by Tycho, the 
Danish astronomer, on the 11th of the following No- 
vember, and the wonder produced by this most extra- 
ordinary phenomenon induced him to give to the star 
the most unremitting attention. Its magnitude in- 
creased until it is said to have surpassed even Jupiter 
in splendor, and finally became visible in the day 
time. It retained its greatest magnitude but for a 
very short time, when it commenced to diminish in 
brilliancy, changing from white to yellow, then to 
reddish, and finally it became faintly blue; and so di- 
minishing by degrees, it vanished from the sight in 
March, 1574, and has never since been seen. 

In the year 1604, while the scholars of Kepler 
were engaged in observations of Mars, Jupiter and 
Saturn, then in close proximity to each other, having 
been interrupted a day or two by clouds, on the re- 
turn of fine weather, Maestlin was astonished to find 
z 2 



294 STRUCTURE OF THE UNIVERSE. 

near the planets then in the constellation Ophiuchus, 
a brilliant star, which certainly had not been there a 
few days before. This object attracted the attention 
of all the great astronomers then living, and was par- 
ticularly observed by Galileo and Kepler. It is said 
to have attained a splendor equal to that of the 
planet Venus, and from this, its greatest brilliancy, it 
gradually declined, until, about the beginning of 1606, 
it ceased to be visible, and no telescopic power 
has since been able to detect any star in the place 
once occupied by this remarkable stranger. 

Although observed with the greatest care, no sensi- 
ble parallax was ever detected in either of these ob- 
jects, and no doubt exists as to their occupying the 
region of the fixed stars. Many other less remarka- 
ble examples are on record, but up to the present no 
satisfactory explanation of this astonishing phenom- 
enon has been given. Whether it indicates the actual 
destruction of some magnificent system, or the revolu- 
tion of these stars in orbits of great eccentricity, caus- 
ing them to appear to us, like the comets, only in the 
perihelion points of their mighty orbits, is equally un- 
certain. One thing is certain : they present evidence 
of change in the starry heavens, of the most startling 
and irresistible kind. 

While new stars have occasionally made their ap- 
pearance, to astonish mankind with their brilliancy, 
there are many well authenticated cases of the entire 
disappearance of old stars, whose places had been 
fixed with a degree of certainty not to be doubted. — 
In October, 1781, Sir William Herschel observed a 
star, No. 55 in Famsted's catalogue, in the constella- 
tion Hercules. In 1790, the same star was observed 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 295 

by the same astronomer, but since that time no search 
has been able to detect it. The star is gone ; whether 
never to return, it is impossible to say. A like dis- 
appearance has occurred with reference to the stars 
numbered 80 and 81, both of the fourth magnitude, in 
the same constellation. In May, 1828, Sir John Her- 
schel missed the star numbered 42 in the constella- 
tion Virgo, which has never since been seen. Exam- 
ples might be multiplied, but it is unnecessary. 

In these cases the stars have been lost entirely ; — 
no return has ever been marked ; and but for the dis- 
covery of another class of remarkable objects among 
the stars, no return would probably ever have been 
suspected. If I could direct your attention to-night 
to a brilliant star named Algol, in the head of Medusa, 
and bring a powerful telescope to aid in your exam- 
inations, this star, while you are watching it, might 
be seen to lose its splendor, and from its rank of the 
second magnitude to decline in brightness, until it 
would scarcely be visible to the naked eye. Having 
reached a certain limit, it would commence an in- 
crease, and by slow degrees resume its original splen- 
dor. — This decrease and increase is actually accom- 
plished in about eight hours. Having regained its 
usual light, it remains stationary for about two days 
and a half, and then repeats the changes already de- 
tailed ; and thus have its periodical fluctuations con- 
tinued since the date of its discovery, with the most 
astonishing regularity. The bright star marked 
Beta, in the constellation Lyra, is known to pass 
from the third to the fifth magnitude, and to regain its 
light in a period of six days and nine hours. These 
are called periodical stars, and a sufficient number 



296 . STRUCTURE OF THE UNIVERSE. 

have already been detected to present a progressively 
increasing series of periods from two days twenty 
hours up to four hundred and ninety-four days, and in 
one case even many years. 

Here, again, are phenomena indicative of extraor- 
dinary activity in these remote regions of space. — 
No explanation of these changes has yet been given 
in all respects satisfactory. Some have attributed 
them to the existence of dark spots on the stars, which, 
by rotation on an axis, periodically present them- 
selves, and thus dim the lustre of the stars. Others 
think the changes are due to the revolution of large 
planets about the stars, which, by coming between 
the eye and the star, eclipse a portion of its light ; 
while a third class conceive the fluctuations to arise, 
in some instances at least, from an orbitual motion of 
the stars in orbits of excessive elongation, and so lo- 
cated as to have their greater axes directed towards 
our system. 

It will be seen that this theory may be readily ex- 
tended so as to embrace the new stars already refer- 
red to, and even to account for those w T hich have been 
lost from their places in the heavens. Here, how- 
ever, we enter the confines of the uncertain. Centu- 
ries may roll away before the true explanation of 
these astonishing changes shall be given ; but the 
mind is on the track, and with a steady and resistless 
movement is slowly pushing its investigations deeper 
and still deeper into the dark unknown. 

While the phenomena of the new and lost stars, 
and the fluctuations in the light of the variable ones, 
gave undeniable evidence of constant change in what 
Aristotle was pleased to call the eternal and incor- 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 297 

ruptible heavens, Herschel's brilliant discovery of the 
orbitual motion of the double stars gave to the mind 
the opportunity of determining the nature of the law 
which sways the movements in these distant regions 
of space. It was natural, in the first efforts to com- 
pute the orbits of the double stars, to adopt the hy- 
pothesis that they attracted each other by the same 
law which prevails in the planetary system. Results 
did not disappoint expectation. — Gravitation, which 
Newton, in the outset of his great discovery, had 
boldly affirmed exerted its influence wherever matter 
existed or motion reigned, was extended, in the 
most absolute manner, to the region of the fixed stars. 
There, at a distance from our own system almost in- 
conceivable, suns and systems of suns, rising in orders 
of greater complexity, revolving with swift velocity, or 
with slow and majestic motion, bore testimony, ample 
and unequivocal, to the truth of the great law of 
universal gravitation. 

Every particle of matter in the universe attracts 
every other particle of matter with a force which is 
proportioned directly to the mass, and which decreases 
as the square of the distance at which it operates in- 
creases. This is no longer a bold hypothesis. The 
double star marked Zeta, in the constellation Hercu- 
les, has been subjected to the analysis of the com- 
puter. The elements of its orbit have been obtained, 
and true to its predicted period, it has actually per- 
formed an entire revolution in a period of thirty-five 
years. The components of the star Eta, in the 
Northern Crown, revolve around their common centre 
in about forty-four years. Both of these pairs have 
completed an entire revolution since their discovery. 



298 STRUCTURE OF THE UNIVERSE. 

Many others might be named, but my only object, at 
present, is to exhibit the evidence which shall remove 
all doubt as to the actual extension of the law of 
gravitation to the fixed stars. 

Let it be remembered that this department of as- 
tronomy is yet in its infancy. Thousands of double 
stars have been detected, and every year adds hun- 
dreds to the list. Among these, a large proportion 
must prove to be binary systems, varying in their 
periods of revolution, from thirty years or less, up to 
many thousands, perhaps millions of years. 

The association of two suns naturally suggests the 
possible union of a greater number, forming more 
complicated systems. This idea has been verified — a 
large number of triple systems has been discovered. 
In a few instances quadruple sets have been found, 
of which a remarkable example exists in the constel- 
lation of the Harp. Here was found four suns, ar- 
ranged in pairs of two. The components of the 
first pair revolve around each other in about one thou- 
sand 3 r ears ; those of the second pair appear to re- 
quire about double that period, while one pair re- 
volves about the other in a period which, determined 
roughly from their distance, cannot fall much below a 
million of years ! The evidence of the physical union 
of these four stars into one grand system rests, at 
present, on the ascertained fact that their proper mo- 
tions are the same. 

From quadruple systems we rise, by analogy, still 
higher, until we find hundreds, sometimes thousands, 
of stars compacted together in so small a compass 
that their proximity cannot be the effect of accident. 
Look at the beautiful little cluster called the Pleiades ; 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 299 

an ordinary eye may here see six or seven stars. One 
of very great power has been known to count four- 
teen in this group, while the telescope increases the 
number to hundreds ; and yet the space in which they 
are located might easily be covered by the moon. 

Suppose an indifferent scattering of the stars 
through space, and compute the chances that such a 
number would fall together at any one point, and we 
shall find not one chance out of millions in favor of 
such an accident. We are therefore forced to the 
conclusion that here is a more magnificent order, one 
in which hundreds of suns, surrounded by their sub- 
ordinate worlds, are all united by gravitation into 
one grand system. This is not a solitary example. — 
Many of these beautiful objects, comparatively close 
to our sun, are found in the heavens, leading the 
mind gradually up to the contemplation and examina- 
tion of that mighty system of systems, that great 
cluster of clusters, the Milky Way. of which all these 
are but subordinate groupings, — vast in themselves, 
but when compared with the whole, mere units 
among the millions of w r hich it is composed. 

From what we have seen, it is impossible to avoid 
the conclusion that gravitation exerts its power 
among the myriads of shining orbs which strew the 
Milky Way. The innumerable suns which form this 
stupendous cluster must feel the reciprocal influence 
of each other, and nothing short of the centrifugal 
force arising from orbitual motion can balance this 
universal attractive power, and give to this grand 
system the great characteristic of stability. 

Herschel succeeded, at least approximately, in sound- 
ing the profundities of the Milky Way, and fixed the 



300 STRUCTURE OF THE UNIVERSE. 

relative position of our own sun among the stars by 
which it is surrounded. He found it to be located 
not very distant from the centre of the great stratum, 
and near the line where the principal current of stars 
divides into two great streams, which for a time sep- 
arate from each other, but finally reunite in a distant 
region of the heavens. 

Having accomplished thus much, this great astrono- 
mer attempted the resolution of the grand problem 
of the sun's movement through space. This investi- 
gation is so lofty, so daring and utterly incomprehen- 
sible at the first glance, that its mere announcement 
produces little effect on the mind. Consider, for one 
moment, what it involves. Man is located on a 
planet almost infinitely larger than himself. This 
planet is swiftly revolving on its axis, and in its orbit 
round a great central luminary, the sun. The daring 
philosopher participates in all these motions. He 
provides himself with instruments which measure the 
distances and positions of the almost infinitely dis- 
tant fixed stars. These fixed stars, when subjected 
to his critical examination, cease to be fixed, and are 
found to be moving with astonishing velocity in all 
directions. Among these he numbers his own sun, 
and although borne along in the progressive motion 
of his own great centre, he ventures to attempt the 
determination of the fact of its actual motion, the di- 
rection in which it moves, and the velocity with 
which it is .sweeping through space. 

This problem is so wonderful that I beg your ear- 
nest attention while the effort is made to simplify 
the reasoning by which its resolution has been 
accomplished. 



MOTIONS AND REVOLUTCONS OF THE FIXED STARS. 301 

Before the actual motions of the earth were dis- 
covered, the sun, moon, and planets, as well as the 
stars, appeared to move in certain directions, and with 
certain velocities, not easily explained. The rotation 
of the earth on its axis rendered a clear explanation 
of the diurnal movements of the heavenly bodies, and 
its orbitual motion around the sun explained the sun's 
apparent annual movement among the fixed stars. — 
Thus it is seen and readily apprehended, that in case 
the spectator is progressing, his actual motion may 
be transferred to distant bodies under examination, 
and these may appear to move while he seems to be 
at rest. 

Now in case the sun is sweeping towards any 
quarter of the heavens, it must carry with it all its 
planets, satellites, and comets. The earth is borne 
along in common with its companions, and the ob- 
server on its surface will transfer his own movement 
through space to the distant objects which only ap- 
pear to change their places, in consequence of his 
own translation through space. Thus the distant 
stars may be affected with a parallactic change, not 
to be confounded with that produced by the revolu- 
tion of the earth in its orbit, but occasioned by the 
fact that while the earth revolves around the sun, she 
is carried forward by this luminary in his journey 
through space. As the whole system participates in 
this motion, in case the planets are inhabited, their 
astronomers will detect in the fixed stars the paral- 
lactic motion due to the sun's movement, and hence 
this change among the stars may be properly termed 
their systematic parallax. 

Herschel commenced his examination of this great 
2 A 



302 STRUCTURE OF THE UNIVERSE. 

problem by forming a catalogue of stars situated in 
all parts of the heavens, in which an appreciable 
amount of proper motion had been detected and meas- 
ured. Now in case this apparent motion of the stars 
could be attributed to the movement of the solar sys- 
tem through space, a close scrutiny of the directions 
in which the stars appeared to move would indicate 
the direction in which the observer, carried along 
with the sun, was passing through space. 

In case a person is traveling on a railway, in a di- 
rect line through a forest of trees, as he advances, all 
objects towards which he is moving will appear to 
open out or separate from each other, while those left 
behind will appear to close up. If, then, the astrono- 
mer, borne along by the movement of the sun through 
the vast forest of stars by which he is surrounded, de- 
sires to ascertain the direction in which he is progres- 
sing, let him search the heavens until he finds a point 
where the stars seem to be increasing their distance 
from each other. Should he find such a point, let 
him confirm his suspicions by looking in the direction 
precisely opposite and behind him, and in case he 
finds the stars located in this region closing up on 
each other, he may fairly conclude that he has found 
the direction in which he is moving, and a rigid co- 
incidence of all the phenomena would demonstrate 
the accuracy of his conclusions. 

Such was the general train of investigation adopted 
by Herschel. After as extended an examination as 
the data with which he was then furnished permitted, 
he announced his belief that a part of the proper 
motion of the fixed stars must be attributed to the 
effect of systematic parallax, and that the solar sys- 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 303 

tem was moving through space towards a point in 
the constellation Hercules. 

The announcement of this astonishing result was 
received with hesitation and doubt by the best living 
astronomers, and Herschel died before any confirma- 
tion of his great theory had been obtained. After his 
death, for nearly half a century, no mind seemed wil- 
ling to renew the investigation. The theory fell into 
disrepute, and was only regarded as a bold and sub- 
lime speculation, but not founded on any well deter- 
mined observations. 

Within a few years, the problem has engaged the 
attention of the distinguished astronomers of Russia. 
Argelander, of Bonn, led the way, and by a train of 
reasoning based upon extensive and accurate obser- 
vations, has sustained and demonstrated, in the most 
undeniable manner, not only the general truth of 
Herschel's theory, but has even confirmed the direc- 
tion in which that astronomer believed the solar sys- 
tem to be moving. 

Here again permit me to attempt a popular expla- 
nation of Argelander's reasoning. Suppose a single 
star to have its place fixed absolutely by observation 
on the first day of the year 1700. One hundred years 
after, its place is again determined, when it is found 
to have shifted its position. Conceive the star to 
have so moved as to reach the meridian earlier than 
it formerly did. When on the meridian, its old place 
will be behind or east of the new place, and a line 
joining the old and new places will show the direc- 
tion in which the star has been moving, and the dis- 
tance between the two places will exhibit the amount 
of motion in one hundred years. If the star do not 



304 STRUCTURE OF THE UNIVERSE. 

move exactly north or south, its line of direction will 
form an angle with the meridian, whose value is de- 
termined from a comparison of the old and new 
places o the star. 

Argelander commenced by selecting five hundred 
stars, in all regions of the heavens, whose places had 
been well determined by preceding astronomers. — 
The preference was of course given to those which 
had been longest subjected to observation. Having 
himself determined the new places of all these stars, 
a comparison of his own with previously observed 
positions, determined the direction in which these 
stars were moving, and their rates of motion. The 
angles formed by the lines along which each star was 
progressing, with the meridian, became known from 
observation, and these angles we shall call the ob- 
served angles of direction. Now it is not difficult to 
compute the directions in which the stars would ap- 
pear to move, if their motion be produced by the 
movement of the solar system. 

Suppose, for example, that the sun, with its plan- 
ets, is sweeping exactly towards the north pole of the 
heavens, then would all the stars appear to move to- 
wards the south. Those in the equator would move 
with the swiftest velocity from the north pole, but 
those nearest the pole would appear to separate from 
each other, while their recess from the pole would be 
comparatively slight. To render this reasoning still 
plainer, imagine this room to be pierced on every 
side, so that an eye placed at the centre could see 
every star in the heavens through the openings. — 
Through each of these holes conceive iron rods to 
pass, all meeting at a point in the centre, and all di- 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 305 

rected exactly to the stars. On the outside let go den 
balls be fixed to the extremities of these rods, to rep- 
resent the stars. Now, grasping the extremities of 
all these rods in the hand, urge the point where they 
ail unite towards the north pole, and watch the move- 
ment of the balls at the outer extremities of the rods. 
The ball corresponding to the north star will scarcely 
seem to move, because the eye travels directly to- 
wards it. The balls corresponding to the stars on the 
equator, having their rods perpendicular to the direc- 
tion of the motion of the central point, will sweep 
swiftly towards the south. The idea once gained, 
there is no difficulty in its application. 

The visual rays drawn to the stars correspond to 
the rods, and these rays, meeting in the eye of the 
observer, are carried forward by the sun in its pro- 
gression through space. I have supposed the sys- 
tem to move due north; but in case the motion be as- 
sumed in any other direction, it is easy to compute 
the changes consequent. Understanding these pre- 
liminary statements, we are prepared to follow Arge- 
lander in his investigation. 

The five hundred stars selected for examination 
were divided into three groups, according to the 
amount of annual proper motion. The first con- 
tained only such stars as were seen to move with a 
velocity not less than one second of space in a year. 
Although this motion may appear excessively slow, 
yet its direction in one hundred years may be deter- 
mined with very great precision. A general examin- 
ation of the direction in which the stars of this first 
group appeared to move, indicated the quarter of the 
heavens towards which the solar system must be pro- 
2 a2 



306 STRUCTURE OF THE UNIVERSE. 

gressing ; and now commenced the investigation, hav- 
ing for its object the discovery of the exact point. — 
To accomplish this, a point was assumed, and on the 
hypothesis that it was correctly chosen, the directions 
of the motion of all the stars composing the first 
group were computed, and the angles formed by their 
lines of direction with the meridian were determined. 

If the motion of these stars was the effect of sys- 
tematic parallax, and if the direction of the solar 
movement had been accurately chosen, then would 
the computed angles of direction agree exactly, in every 
instance, with the observed angles of direction. The 
comparison of these angles having been made, it was 
easy to see the discrepancies, and by shifting the as- 
sumed point, these differences could be reduced to 
their minimum value. The point which gave the 
smallest differences between the observed and com- 
puted angles would be the one towards which the so- 
lar system was progressing. Such was the reasoning 
of iVrgelander, and such the train of investigation on 
which he relied for the resolution of this great 
problem. 

Having closed his examinations based on the group 
of stars with the most rapid motion, and having found 
the point in the heavens which corresponded to their 
motions, he proceeded to execute his calculations with 
reference to his second group. The stars of this group 
moved annually an amount greater than half a second 
of space, and less than one second. The result was 
again reached, and the direction of the solar motion 
thus derived, agreed, in a remarkable manner, with 
that obtained from the first group. A further confir- 
mation was obtained by executing the calculation 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 307 

founded on the motions of the third and last group 
into which he had divided his five hundred stars. — 
The final result settled, probably forever, the grand 
fact that the sun, with its entire cometary and plane- 
tary system, is sweeping through space towards a 
point whose place must fall somewhere within the 
circumference of a circle whose diameter is about 
equal to four times that of the moon. 

The reality of the solar motion once determined, 
astronomers have not been wanting to verify and ex- 
tend this wonderful examination. Argelander's re- 
sults have been confirmed by the investigations of M. 
Otho Struve, the son of the distinguished director of 
the Imperial Observatory of Pulkova ; and if, on any 
fair night, you direct your eye to the constellation 
Hercules, and select from its stars the two marked 
on the globe with the Greek letters * and fi, on 
the line joining these stars, and at a distance from * 
equal to one-quarter of the distance which divides 
the stars will be found the point towards which the 
sun was directing his course in the year 1840. 

Having obtained the direction of the solar motion, 
we proceed to investigate its actual velocity. How 
swiftly does the sun, with its retinue of worlds, sweep 
onward through space ? It will not be possible to 
present here even an outline of the reasoning of 
Struve in the resolution of this intricate question. — 
Two points are involved. The determination of 
the annual angular motion of the sun, as it would be 
seen by a spectator situated at a distance equal to 
that of the stars of the first magnitude. This being 
determined, the angular motion can readily be con- 
verted into linear velocity, in case the mean distance 



308 STRUCTURE OF THE UNIVERSE. 

of the stars of the first magnitude can be satisfacto- 
rily obtained. After an elaborate investigation, 
guarded by every care, and open, as it would appear, 
to no well founded objections, M. Otho Struve has 
finally resolved the first of these wonderful questions. 
It is curious to see how nearly the results agree, which 
were obtained from data entirely different, and in no 
way dependent on each other. 

By an examination based on observed right ascen- 
sions of the stars, he finds that the space passed over 
by the sun in its progressive movement through the 
heavens, seen from the mean distance of stars of the 
first magnitude, is three hundred and twenty-one- 
thousandths of a second of arc. The result obtained 
from observed declinations gave for the same quantity 
three hundred and fifty-seven-thousandths of one 
second of arc. Here is a difference amounting to 
only thirty-six-thousandths of a second, a quantity 
exceedingly small, when we consider the extraordi- 
nary difficulty of the investigation. 

Let us now convert these numbers into intelligible 
quantities. In case the sun be supposed to be revolv- 
ing about some mighty centre, at a distance equal to 
the mean distance of stars of the first magnitude, the 
period necessary to accomplish its stupendous revolu- 
tion will be 3,811,000 years ! 

Vast as this period appears, we shall see hereafter 
that we have no right to suppose that the centre about 
which the solar system is revolving, can be located at 
a distance nearty so small as the mean distance of 
the larger stars. But what is the actual velocity ? — 
How many miles does this mighty assemblage of fly- 
ing worlds accomplish in its unknown journey in 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. o09 

every year ? This is the last question, and even this 
has not escaped the successful examinations of the 
human mind. The discovery of the parallax of one 
or two fixed stars has already been referred to. — 
Within a few months, an elaborate work, by Struve, 
on the Sidereal Heavens, has reached us, containing 
some remarkable investigations on the mean distances 
of the stars of the various magnitudes. 

Struve, by a most ingenious and powerful train of 
investigation, obtains a series representing the relative 
mean distances of the stars of all magnitudes, up to 
the most minute visible in Herschel's twenty feet re- 
flector. From the sun, as a centre, he sweeps succes- 
sive concentric spheres, between whose surfaces he 
conceives the stars of the several magnitudes to be 
included. The radius of the first sphere reaches to 
the nearest stars of the first magnitude ; that of the 
second sphere extends to the farthest stars of the same 
magnitude, and the mean of these two radii will be 
the mean distance of the stars of the first magnitude. 
The same is true with reference to the concentric 
spheres embracing within their surfaces the stars of 
the various orders of brightness. 

Having, from his data, computed a table exhibiting 
the relative distances of the stars of the different mag- 
nitudes, an examination of these figures revealed 
the singular fact that they constituted a regular ge- 
ometrical progression ; and having assumed the dis- 
tance of the stars of the sixth magnitude as the unit, 
the distance of the stars of the fourth magnitude will 
be one-half ; that of those of the second magnitude 
will be one-quarter, and so of the even numbers ex- 
pressing magnitude ; while the distance of the stars of 



310 STRUCTURE OF THE UNIVERSE. 

the fifth magnitude is obtained by dividing unity by 
the square root of the number 2, and from this the dis- 
tances of the odd magnitudes come by dividing con- 
stantly by 2. In mathematical language, the distances 
of the stars of the various magnitudes form a geom- 
etrical progression whose ratio is equal to unity di- 
vided by the square root of 2. 

Having thus obtained the relative mean distances 
of the stars, in case we can find the absolute mean 
distance of those of any one class, that will reveal to 
us the absolute mean distances of the stars of every 
class. For the approximate accomplishment of this 
last great object, we are again indebted to the as- 
tronomers of Russia. As early as 1808, M. Struve, 
then of Dorpat, attempted the determination of the 
parallax of a large number of stars, and obtained re- 
sults so small that, in the state of astronomical sci- 
ence as it then existed, no confidence could be placed 
in them. The final value of the numerical co-effi- 
cient of the aberration of light had not been then ab- 
solutely determined. Subsequent investigations by 
Struve and Peters have fixed this quantity, and the 
actual determination of the parallax of eight stars 
recently, has shown that confidence may now be 
placed in the results obtained by Struve nearly 25 
years ago. 

By combining all the results, M. Peters finds no less 
than thirty-five stars whose parallaxes have now 
been determined, either absolute or relative, with a 
degree of accuracy which warrants their employment 
in investigating the problem of the mean parallax 
of stars of the second magnitude. Excluding from 
this number the stars 61 Cygni, and No. 1830 of the 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 311 

Grombridge catalogue, on account of their great 
proper motion, there remained thirty-t'-iree stars to 
be emplo} r ed in the investigation. 

From a fall and intricate examination of all the 
data, by a process of reasoning which I will not attempt 
to explain at this time, M. Peters finds the mean par- 
allax of stars of the second magnitude to be equal to 
116 thousandths of one second of arc, with a probable 
error less than a tenth part of this quantity. Return- 
ing now, with this absolute result, to the table of 
the relative distances of the fixed stars of different 
magnitudes, it is easy to fix their absolute distances, 
as far as confidence can be placed in this first 
approximation. We find the stars of the first magni- 
tude to be located between the surface of two spheres, 
whose radii are respectively nine hundred and eighty- 
six thousand times the radius of the earth's orbit, and 
one million two hundred and forty-six thousand 
times the same unit. We will express the distance 
in terms of the velocity of light, as no numbers can 
convey any intelligible idea. Stars of the first mag- 
nitude send Us their light in about seventeen years ; 
those of the second magnitude in about thirty years ; 
— stars of the third magnitude send their light in 
about forty-five years ; those of the fourth magnitude 
in sixty-five years ; those of the fifth in ninety years; 
those of the sixth magnitude, the most remote visible 
to the naked eye, send us their light after a journey 
through space of one hundred and thirty years ! while 
the distance of the lowest order of telescopic stars 
visible in Herschel's twenty feet reflector is such, that 
their light does not reach the eye for 3,541 years after 
it starts on its tremendous journey ! 



3] 2 STRUCTURE OF THE UNIVERSE. 

Let it be remembered that these results are not 
conjectures. Though they are first approximations 
to the truth, they are reliable to within the tenth part 
of their value, and are thus far certain ; they raise, in 
the most astonishing manner, our views of the im- 
mensity of the universe, and of the powers of human 
genius which have fathomed these vast and over- 
whelming profundities. 

Let us now return to the examination of the abso- 
lute amount of progressive motion of our sun and 
system through space. As already stated, M. Otho 
Struve determined its yearly angular motion, as seen 
from the more distant of the stars of the first magni- 
tude. To convert this angular motion into miles, a 
knowledge must be obtained of the absolute mean 
distance of the stars of the first magnitude. This has 
been accomplished by M. Peters, and combining the 
researches of Argelander, Struve, and Peters, we are 
now able to pronounce the following wonderful re- 
sults. — The sun, attended by all its planets, satellites, and 
comets, is sweeping through space towards the star marked 
7t in the constellation Hercules, with a velocity which causes 
it to pass over a distance equal to thirty-three millions three 
hundred and fifty thousand miles in every year ! 

And now do you demand how much reliance is to 
be placed on this bewildering announcement ? I an- 
swer, that as to the reality of the solar motion, there 
is but one chance out of four hundred thousand that 
astronomers have been deceived. We cannot resist 
the evidence, and startling as the truth appears, we 
are obliged to yield our assent, reluctant though it 
may be, to the logical reasoning by which this mag- 
nificent result has been demonstrated. 



MOTIONS AND REVOLUTIONS Of THE FIXED STARS. 313 

But whither is our system tending ? If moving on- 
ward with such tremendous velocity, is there not danger 
that ere long it may reach the region of the fixed stars, 
and by sweeping near to other suns and systems, de- 
range the order of the planetary worlds ? Let us exam- 
ine this question for one moment, on the hypothesis that 
the sun alone is moving among all the stars of hea- 
ven, and that it will hold on in its present direction 
until it shall reach the star in Hercules, towards 
which it is now urging its flight. This star is of the 
third magnitude, and according to our statement al- 
ready made, the mean distance of its class is such, 
that its light does not reach us in a period less than 
forty-six years. Executing the calculation, we find 
that in case the solar system should continue to pro- 
gress towards that star, it cannot pass the enormous 
interval, even at 33,550,000 miles per annum, in less 
than 1,800,000 years! 

If the eye of any superior intelligence can behold 
this amazing scene, how stupendous must be the spec- 
tacle presented ! In the centre the sun, blazing with 
splendor, pursues its majestic career; — around it roll 
the planets, and about it cluster ten thousand fiery 
comets. Worlds bright and beautiful hover near the 
sun , — worlds fiery and chaotic seek this great centre 
with impetuous velocity, and then dash away into 
the farthest range of their grand revolution. But the 
monarch moves on, and his magnificent cortege, per- 
forming his high behests, follow whithersoever he 
leads through space ! 

Here we reach the boundary which divides the 
known from the unknown. Steadily we have pur- 
sued the human mind, as it has moved on in its grand 
2B 



314 STRUCTURE OF THE UNIVERSE. 

researches of the universe of God. Time, and space, 
and number, and distance, have all been set at defi- 
ance. No limits have been sufficiently great to cir- 
cumscribe its movement. For more than six thousand 
years, onward ! has truly been the word. And here I 
might very well pause, and rest content in the exhibi- 
tion of the absolute and actual triumphs of human 
genius ; but as the rays of the rising sun penetrate 
the darkness of night, and scattering the gloom, dimly 
reveal the scenes of earth which are soon to be flooded 
with splendor, so the light of human knowledge breaks 
over the boundaries which divide the known from the 
unknown, and faintly reveals what yet lies far beyond 
in the dark profound. 

Guided by this light, we shall ask your attention to 
one of the most sublime speculations to which the 
mind of man has ever risen. I refer to the supposed 
discovery of the great centre about wilich it is pre- 
sumed the myriads of stars composing our mighty 
Milky Way are all revolving. 

M. Maedler, the author of the recent investigations 
with reference to the Central Sun, has long been 
known to the astronomical world as the successor of 
M. Struve in the direction of the observatory at Dor- 
pat. His computations of the orbitual movements of 
the double stars have given to him a deservedly high 
celebrity, and the great theory which he has propoun- 
ded is only given to the world after a long and patient 
examination, extending through seven years. 

The extension of the law of gravitation to the fixed 
stars, now absolutely demonstrated in the revolutions 
of the binary systems, settles forever the fact, that in 
the grand association of stars composing our cluster, 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 315 

or, as we shall hereafter call it, our astral system, there 
must be a centre of gravity, as certainly as there is one 
to the solar system. In the organization of the solar 
system we find a central body of vast size, surrounded 
by small and subordinate satellites. Again, among 
the planets, we find their magnitude very great, when 
compared with the moons which circulate around 
them. Extending this analogy, early astronomers 
conceived that this principle of a great central pre- 
ponderating globe would, in all probability, obtain in 
all the higher orders of physical organization. 

This idea, apparently so well founded, was entirely 
destroyed by the discovery of the binary stars. Here 
we find the next higher organization above our solar 
system, but instead of finding in the bodies thus 
united a vast preponderance in magnitude of one 
over the other, there are many examples in which the 
two suns thus united by gravitation are, in all re- 
spects, equal. In many others the difference is only 
slight, yet in all these higher systems there must exist 
a common centre of gravity. 

With the mind cleared, by these views, from all 
prejudice in favor of the necessary existence of some 
stupendous central globe, as far exceeding in magni- 
tude the myriads of fixed stars by which it is sur- 
rounded as does the sun all the satellites of its sys- 
tem, we are prepared to inquire into the actual exis- 
tence or nonexistence of such a body. 

Admitting its invisibility, either in consequence of 
its distance or nonluminous character, there are yet 
remaining the means, not only of detecting its exist- 
ence, but of discovering its position in space. In case 
such a body exists, the stars located nearest to it will 



316 STRUCTURE OF THE UNIVERSE. 

be most completely subjected to its influence, and 
will show their proximity by the swiftness of their 
motion. Since it is possible to penetrate space in 
every direction, in case the stars of any particular re- 
gion were endowed with a more rapid motion than 
all others, these would not fail to be discovered. But 
no such rapid motions have ever been detected, and 
hence it is now fair to conclude that such motions do 
not exist, and consequently no vast central globe can 
ever be found, because there is no evidence that such 
a body has any locality in space. 

The question resolves itself, then, into a research 
for the common centre of gravity of all the stars com- 
posing our astral system, and the data for such an 
examination must be found in the direction of the 
solar motion, and in that of the proper motion of the 
fixed stars. Difficult as this research undoubtedly 
is, Maedler's sagacity detected various guides which 
limited his more minute examinations to a compara- 
tively small portion of the heavens. Since our great 
astral system has been shown to take the form of a 
layer or stratum whose thickness is small compared 
with its extent, we cannot fail to perceive that the 
centre of gravity of a mass of stars thus arranged 
must be found somewhere within the limits of the 
Milky Way, when seen by an eye located not very 
distant from the centre. But it is seen that our sun 
does not occupy the absolute centre of this stratum. 
In case it did, then would the bright circle of the 
Milky Way divide the heavens into two equal hemis- 
pheres. Since there is a manifest difference between 
the two parts into which the heavens is divided, the 
smaller portion will be the more distant from us, and 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 317 

in this smaller part we must look for the central 
point. But, from the soundings of both the Herschels, 
it is certain that our sun lies nearer the southern half 
of the Milky Way than the northern. Hence, in our 
researches for the centre of gravity, we may confine 
our examinations to the northern half of the smaller 
of the two parts into which the Milky Way divides 
the heavens. 

One more approximation may be made. If we 
knew that our sun, in its presumed revolution about 
this great centre, described a circle, and if we knew 
the plane of this circle, and the direction in which the 
sun was now moving, a line drawn in that plane from 
the sun, and in a direction perpendicular to its line of 
motion, would pass directly through the centre about 
which it is revolving, and would point us directly to 
it. Now the direction of the sun's motion is alone 
determined ; but since the centre of gravity must be 
found somewhere in a line perpendicular to the direc- 
tion, we must give to this perpendicular all possible 
positions in space, which will cause it to cut from the 
celestial sphere the circumference of a great circle, 
within which the centre of gravity must be found. — 
These limiting considerations brought the distin- 
guished astronomer to a region of the heavens in and 
about the constellation Taurus. 

Here the examination took a more definite and 
more strictly scientific form. The proper motion of 
the stars in this region could be anticipated and 
known, at least in character and direction. The 
great centre would probably be located within the 
limits of some rich cluster. All the stars composing 
this cluster, as well as those within 20° or 30°, would 
2 b 2 



318 STRUCTURE OF THE UNIVERSE. 

appear to move in the same direction. Those im- 
mediately proximate to the central sun or star would 
appear to move with the same velocity due to that 
star, and the entire group would sweep, apparently, 
through space without parting company. 

Having, by such like considerations, narrowed 
down the limits of research, Maedler commenced his 
individual examinations. Among other objects sub- 
jected to rigid scrutiny, was the brilliant star Alde- 
baran, in the eye of the Bull. This being the bright- 
est star in this region, and being, moreover, in the 
midst of a group of smaller stars, seemed, in the oat- 
set, to fulfill some of the conditions required of the 
central sun. But a more rigid examination proved 
conclusively that this star could not occupy the centre. 
Its own proper motion far exceeded that of the sur- 
rounding stars, and demonstrated its near proximity 
to our own system, and its mere optical connection 
with the stars surrounding it. 

Thus did this great astronomer move from point to 
point, from star to star, subjecting each successively 
to the severest tests, until, finally, a point was found, 
a star was discovered, fulfilling, in the most remarka- 
ble manner, all the requisitions demanded by the na- 
ture of the problem. All are familiar with the beau- 
tiful little cluster, called the Pleiades, or seven stars. 
Clustered around the brilliant star Alcyone, which oc- 
cupies the optical centre of the group, the telescope 
shows fourteen conspicuous stars. The proper mo- 
tions of all these have been determined with great ex- 
actitude. These are all in the same direction, and are 
all nearly equal to each other ; and, what is still more 
important, the mean of their proper motions differs 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 319 

from that of the central star, Alcyone, by only one- 
thousandth of a second of arc in right ascension, and 
by two-thousandth's of a second in declination. — 
Here, then, is a magnificent group of suns, either ac- 
tually allied together, and sweeping in company 
through space, or else they compose a cluster so situ- 
ated as to be affected by the same apparent motion 
produced by the sun's progressive motion through 
the celestial regions. 

But an extension of the limits of research around 
Alcyone exhibits the wonderful truth, that out of one 
hundred and ten stars within 15° of this centre, there 
are sixty moving south, or in accordance with the hy- 
pothesis that Alcyone is the centre, forty-nine exhibit- 
ing no well defined motion, and only one single in- 
dividual which appears to move contrary to the com- 
puted direction ! 

It is impossible, here, to do justice to the profound 
and elaborate investigations of the learned author of 
this great speculation. Assuming Alcyone as the 
grand centre of the millions of stars composing our 
astral system, and the direction of the sun's motion, 
as determined by Argelander and Struve, he investi- 
gates the consequent movements of all the stars in 
every quarter of the heavens. Just where the swift- 
est motions should be found, there they actually exist, 
either demonstrating the truth of the theory, or exhib- 
iting the most remarkable and incredible coincidences. 
We shall not pursue the research. After a profound 
examination, Maedler reaches the conclusion that Al- 
cyone, the principal star in the group of the Pleiades, 
now occupies the centre of gravity, and is at present the 



320 STRUCTURE OF THE UNIVERSE. 

sun about which the universe of stars composing our as- 
tral system are all revolving. 

Here, then, we stand on the confines of the un- 
known. One mighty effort has thus been made to 
bring beauty and order out of the chaos of motion 
which has hitherto distinguished the stars of heaven. 
Once the planets, freed from law, darted through 
space, or relaxing their speed, actually turned back 
on their unknown routes. Chaos reigned among these 
flying globes until the mind, rising by the efforts of 
its own genius, reached the grand centre of the plan- 
etary orbs, and lo ! confusion ceased, and harmony 
and beauty held their sway among these circling 
worlds. The same daring human genius which, 
sweeping across the interplanetary spaces, finally 
reached the controlling centre of our own great sys- 
tem, has now boldly plunged into the depths of space, 
has swept across the interstellar spaces, and roam- 
ing from star to star, from sun to sun, from system to 
system, looks out upon the universe of stars, and 
seeks that point from whence these millions of sweep- 
ing suns shall exhibit that grand and magnificent 
harmony which doubtless reigns throughout the vast 
empire of Jehovah. 

We are too apt to turn away from the first efforts 
to resolve these mighty problems. How were the 
doctrines of Newton received? How much regard 
was paid to Herschel's grand theory of the solar mo- 
tion ? And yet how triumphantly have these great 
theories been established. But do you inquire if there 
be any possibility of proving or disproving the doc- 
trines of Maedler? The answer is simple. Should 
the time ever come when the direction of the solar 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 321 

motion shall be sensibly changed, in consequence of 
its curvilinear character, then will the plane in which 
this movement lies be revealed, and then the centre 
about which the revolution is performed must be 
made known, at least in direction. Should the line 
reaching towards this grand centre pass through Al- 
cyone, this added to all the other evidences, will fix 
forever the question of its central position. We know 
not when this great question may be settled, but judg- 
ing from the triumphs which have marked the career 
of human genius hitherto, we do not dare to doubt 
of the final result. 

Admitting the truth of Maedler's theory, we are led 
to some of the most astonishing results. The known 
parallax of certain fixed stars gives to us an approxi- 
mate value of the parallax of Alcyone, and reveals to 
us the distance of the grand centre. Such is the 
enormous interval separating the sun from the central 
star about which it performs its mighty revolution, 
that the light from Alcyone requires a period of 537 
years to traverse the distance ! And if we are to rely 
on the angular motion of the sun and system, as al- 
ready determined, at the end of 18,200,000 years, this 
great luminary, with all its planets, satellites, and 
comets, will have completed one revolution around its 
grand centre ! 

Look out to-night on the brilliant constellations 
which crowd the heavens. Mark the configurations 
of these stars. Five thousand years ago the Chal- 
dean shepherd gazed on the same bright groups. — 
Two thousand years have rolled away since the 
Greek philosopher pronounced the eternity of the 
heavens, and pointed to the ever-during configuration 



322 STRUCTURE OF THE UNIVERSE. 

of the stars as proof positive of his assertion. But a 
time will come when not a constellation now blazing 
in the bright concave above us shall remain. Slowly, 
indeed, do these fingers on the dial of heaven mark 
the progress of time. A thousand years may roll 
away with scarce a perceptible change ; — even a mil- 
lion of years may pass without effacing all traces of 
the groupings which now exist ; but that eye which 
shall behold the universe of the fixed stars when ten 
millions of years shall have silently rolled away, will 
search in vain for the constellations which now beau- 
tify and adorn our nocturnal heavens. Should God 
permit, the stars may be there, but no trace of their 
former relative positions will be found ! 

Here I must close. The intellectual power of man, 
as exhibited in his wonderful achievements among the 
planetary and stellar worlds, has thus far been our 
single object. I have neither turned to the right hand 
nor to the left. Commencing with the first mute gaze 
bestowed upon the heavens, and with the curiosity 
awakened in that hour of admiration and wonder, we 
have attempted to follow rapidly the career of the hu- 
man mind, through the long lapse of six thousand 
years. What a change has this period wrought. Go 
backward in imagination to the plains of Shinar, and 
stand beside the shepherd astronomer as he vainly 
attempts to grasp the mysteries of the waxing and 
waning moon, and then enter the sacred precincts of 
yonder temple devoted to the science of the stars. — 
Look over its magnificent machinery ; examine its 
space-annihilating instruments, and ask the sentinel 
who now keeps his unbroken vigil, the nature of his 
investigations. 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. 323 

Moon, and planet, and sun, and system, are left be- 
hind. His researches are now within a sphere to 
whose confines the eagle glance of the Chaldean 
never reached. Periods, and distances, and masses, 
and motions, are all familiar to him, and could the 
man who gazed and pondered six thousand years ago 
stand beside the man who now fills his place, and 
listen to his teachings, he would listen with awe, in- 
spired by the revelations of an angel of God. But 
where does the human mind now stand ? Great as 
are its achievements, profoundly as it has penetrated 
the mysteries of creation, what has been done is but 
an infinitesimal portion of what remains to be done. 

But the examinations of the past inspire the high- 
est hopes for the future. The movement is one con- 
stantly accelerating and expanding. Look at what 
has been done during the last three hundred years, 
and answer me to what point will human genius 
ascend, before the same period shall again roll away? 
But in our admiration for that genius which has been 
able to reveal the mysteries of the universe, let us 
not forget the homage due to Him who created, and 
by the might of his power sustains all things. At 
some future time, I hope to be permitted to direct 
your attention to this branch of the subject. If there 
be anything which can lead the mind upward to the 
Omnipotent Ruler of the universe, and give to it an 
approximate knowledge of His incomprehensible attri- 
butes, it is to be found in the grandeur and beauty of 
His works. 

If you would know his glory, examine the intermi- 
nable range of suns and systems which crowd the 
Milky Way. — Multiply the hundred millions of stars 



324 STRUCTURE OF THE UNIVERSE. 

which belong to our own " island universe " by the 
thousands of these astral systems that exist in space, 
within the range of human vision, and then you may 
form some idea of the infinitude of his kingdom ; for 
lo ! these are but a part of his ways. Examine the 
scale on which the universe is built. — Comprehend, 
if you can, the vast dimensions of our sun. — Stretch 
outward through his system, from planet to planet, 
and circumscribe the whole within the immense cir- 
cumference of Neptune's orbit. This is but a single 
unit out of the myriads of similar systems. Take 
the wings of light, and flash with impetuous speed, 
day and night, and month, and year, till youth shall 
wear away, and middle age is gone, and the extremest 
limit of human life has been attained ; — count every 
pulse, and at each speed on your way a hundred 
thousand miles; and when a hundred years have 
rolled by, look out, and behold ! the thronging millions 
of blazing suns are still around you, each separated 
from the other by such a distance that in this journey 
of a century you have only left half a score behind 
you. 

Would you gather some idea of the eternity past 
of God's existence, go to the astronomer, and bid him 
lead you with him in one of his walks through space; 
and as he sweeps outward from object to object, from 
universe to universe, remember that the light from 
those filmy stains on the deep pure blue of heaven, 
now falling on your eye, has been traversing space 
for a million of years. Would you gather some 
knowledge of the omnipotence of God. weigh the 
earth on which we dwell, then count the millions of 
its inhabitants that have come and gone for the last 



MOTIONS AND REVOLUTIONS OF THE FIXED STARS. o'25 

six thousand years. Unite their strength into one 
arm, and test its power in an effort to move this 
earth. It could not stir it a single foot in a thou- 
sand years ; and yet under the omnipotent hand of 
God, not a minute passes that it does not fly for more 
than a thousand miles. But this is a mere atom ; — 
the most insignificant point among his innumerable 
worlds. At his bidding, every planet, and satellite, 
and comet, and the sun himself, fly onward in their 
appointed courses. His single arm guides the mil- 
lions of sweeping suns, and around His throne circles 
the great constellation of unnumbered universes. 

Would you comprehend the idea of the omniscience 
of God, remember that the highest pinnacle of knowl- 
edge reached by the whole human race, by the com- 
bined efforts of its brightest intellects, has enabled 
the astronomer to compute approximately the pertur- 
bations of the planetary worlds. He has predicted 
roughly the return of half a score of comets. But 
God has computed the mutual perturbations of mil- 
lions of suns, and planets, and comets, and worlds, 
without number, through the ages that are passed, 
and throughout the ages which are yet to come, not 
approximately, but with perfect and absolute pre- 
cision. The universe is in motion, — system rising 
above system, cluster above cluster, nebula above 
nebula, — all majestically sweeping around under the 
providence of God, who alone knows the end from 
the beginning, and before whose glory and power 
all intelligent beings, whether in heaven or on earth, 
should bow with humility and awe. 

Would you gain some idea of the wisdom of God, 
look to the admirable adjustments of the magnificent 
2 C 



326 STRUCTURE OF THE UNIVERSE. 

retinue of planets and satellites which sweep around 
the sun. Every globe has been weighed and poised, 
every orbit has been measured and bent to its beauti- 
ful form. All is changing, but the laws fixed by the 
wisdom of God, though they permit the rocking to and 
fro of the system, never introduce disorder, or lead to 
destruction. All is perfect and harmonious, and the 
music of the spheres that burn and roll around our 
sun, is echoed by that of ten millions of moving 
worlds, that sing and shine around the bright suns 
that reign above. 

If overwhelmed with the grandeur and majesty of 
the universe of God, we are led to exclaim with the 
Hebrew poet king, — "When I consider thy heavens, 
the work of thy fingers, the moon and the stars which 
thou hast ordained, what is man, that thou art mind- 
ful of him ? and the son of man, that thou visitests 
him ? " If fearful that the eye of God may overlook 
us in the immensity of his kingdom, we have only to 
call to mind that other passage, "Yet thou hast 
made him but a little lower than the angels, and hast 
crowned him with glory and honor. Thou madest 
him to have dominion over all the works of thy hand ; 
thou hast put all things under his feet." Such are 
the teachings of the word, and such are the lessons 
of the works of God. 



DESCRIPTION OF THE TELESCOPIC VIEWS. 

PLATE I. 

Halley's Comet, as figured by Sir John Herschel, at the Cape of Good 
Hope. Oct. 29, 1835. 

The rapid changes in this extraordinary object, at its last appearance, 
have attracted great attention among astronomers. Sir John Herschel 
describes its appearance, at the date of the drawing, as follows : 

" Its nucleus small, bright and highly condensed, was shielded, or capped f 
on the side next the sun, by a vivid, but narrow crescent of nebulous light, the 
front of which presented an outline nearly circular, having an amplitude of 
somewhat more than 90° from horn to horn. Within this was situated 
the nucleus, at a distance behind the vertex, such that the homs of the 
crescent extended a good way behind the nucleus, on either side. * * * 
The nucleus was decidedly not planetary, and as decidedly exhibited no phase. 
As the evening advanced, the exterior strata of the crescent — the coma and 
the tail which were before obliterated by the twilight — became visible, and 
the whole finally put on the appearance represented in Plate I." 

From this time to the month of January, 1 836, many changes are noted. 
During part of the time a necessary absence from the observatory, suspended 
observations. They were resumed, and continued up to the final disappear- 
ance of the comet. 



PLATE II. 



Halley's Comet, as figured by Sir John Herschel, at the Cape of Good 
Hope. Jan. 28, 1836. 

Sir John Herschel uses the following language: 
« Most astonishing ! The coma is all but gone, but there are long irregu- 

C327) 



328 DESCRIPTION OF THE TELESCOPIC VIEWS. 

lar nebulous tails in various directions. The nucleus is now no longer a dim 
misty speck, but a sharp brilliant point. I cannot, however, * raise a disc ' 
on it, at least a well denned one ; but the light comes on so suddenly, it is like 
a planetary nebula, a little hazy at the edges, 2 or 2^ seconds in diameter. 
* * * Being now high, and the telescope acting to admiration, I see a 
sharp, all but planetary, disc, diameter fully H seconds, quite distinct from 
the haze about it. Power 320 shows it well. It is like one of Jupiter's 
satellites in a thick fog of hazy light. Nothing can be more delicate and 
regular than the curve of the head, and the symmetry of the whole upper 
part of the figure." * * * The observations of this night conclude with the 
following memorandum : — "So ended a most remarkable night. I can 
hardly doubt that the comet has fairly evaporated in perihelia, by the heat, 
and resolved into transparent vapor, and is now in process of rapid conden- 
sation and reprecipitation on the nucleus." 

The drawings of Herschel are numerous, and exhibit the progressive 
changes in the dimensions of the comet. Two only have been selected as 
specimens. 



PLATE III. 



Halley's Comet, as figured by Struve, Director of the Imperial Obser- 
vatory, Polkava, Russia. Oct. 12, 1835. 

The comet was observed and drawn with great care, by Prof. Struve. 
He has published a large work, containing all his observations and drawings, 
from which the plate in this volume is copied, and the following notices are 
translated. " On the setting of the moon the clouds dispersed, and the comet 
appeared for a short time in great beauty. Soon the heavens were again 
covered with light clouds, through which all the parts of the comet were 
concealed, except the nucleus and flame, which remained distinctly visible. 
The appearance of the flame was wonderful. It resembled a ray of fire 
shot out from the nucleus, as from some engine of artillery, and driven on 
one side by the wind. Nearly in the opposite direction a second emanation, 
or flame, more faint than the first, was visible. The clouds prevented 
farther observation on that evening." 



DESCRIPTION OF THE TELESCOPIC VIEWS. 329 

The beautiful symmetry exhibited in this drawing, must attract every 
eye. Nothing can be more delicate than the forms and bounding curves of 
these singular appendages to the comet. The nucleus is sharp and well 
defined, and from it emanate these strange gaseous out-shoots. The rapid 
changes noted by Herschel, are equally represented in the drawings 
of Struve. 



PLATE IV. 

The Great Comet of 1744. 

This object is one of the most remarkable among the comets. It is not 
uncommon for two tails to present themselves, but a display of six luminous 
trains, of vast extent, has, so far as I know, never been witnessed, except in 
this case. The spaces between the tails are represented, by the writers of the 
day, as having been as dark as the heavens, while each tail was bordered by 
a luminous edging of great beauty. The enclosed space was faintly illumina- 
ted. The tail was no where bright enough to produce the slightest effect on 
the appearance of the fixed stars, as seen through it. Their light was not, 
in the smallest degree, dimmed. 

After the head of the comet had sunk below the horizon, these brilliant 
trains of light, radiating from a common point, were long visible, presenting 
a most wonderful appearance. I am not aware that the period of this body 
has ever been determined. 



PLATE V 



A Globular Cluster of Stars in the Constellation of Hercules. A. R. 
15 h. 36 m. N. Dec. 36° 46'. 

This object, one of the most beautiful in the heavens, was discovered by 
Halley, as far back as 1714. It was regarded by its discoverer as a nebula, 
and was not known to contain any stars. This is remarkable, as a very 
moderate power suffices to exhibit its stellar characteristics, while the great 
instruments of modern times exhibit within its limits a countless multitude 

2 c2 



330 DESCRIPTION OF THE TELESCOPIC VIEWS. 

of stars, condensing towards the center into a glow of great brilliancy and 
beauty. This is doubtless one of the " Island Universes '' found in space, 
and of an extent not inferior to that of the Milky Way. The heavens, as 
seen from a sun of this astral system, near its center must present a most 
gorgeous appearance. In all directions may be seen innumerable stars 
of all magnitudes, forming a spectacle such as would be presented by our 
heavens, in case the Milky Way were expanded to cover the entire celestial 
sphere. I have examined this object with the great Refractor of the Cincin- 
nati Observatory, on many occasions, and the engraving is made from one 
of my drawings. No one can behold this magnificent object, for the first 
time, without exclamations of wonder and astonishment. The whole extent 
is embraced at once in the field of the large telescope, with a power of 250. 



PLATE VI. 

Lord Rosse's Crab Nebula. 
This object had long been known as a faint, ill defined, nebula of an 
elliptical figure, with nothing to distinguish it from many other similar 
luminous clouds. When examined by Lord Rosse's three feet reflector, its 
aspect was entirely changed. The central part was seen to be composed of 
a vast multitude of stars, while branching filaments of hazy light extended 
from the center, in all directions. There can be little doubt of the actual 
character of this singular object. It is probably an immense cluster of suns, 
of a figure which seems to bid defiance to all our ideas of regularity or order. 
As it still rests on a bed of misty light, indicating still more distant portions 
of it, a higher power may hereafter work a complete change in the character 
of its outline. It is among the most distant objects visible in the telescope, 
and exhibits a specimen of the singular variety of form, occasionally shown 
among these vast congeries of stars. 



PLATE VII. 
The Great Nebula in Orion. R. A. 5 h. 27 m. Decl. S. 5° 30'. 
Discovered by Huygens in 1656. It is one of the largest among the 



DESCRIPTION OF THE TELESCOPIC VIEWS. 331 

nebula, and certainly one of the most magnificent. It was examined by the 
elder Herschel, with the entire range of his telescopic power, without ex- 
hibiting any appearance of being composed of stars. Within the outline of 
the nebula there are a great many large and brilliant stars, but these are 
undoubtedly between the eye and the nebula, and in no way connected with 
it. Among these stars there is one marked on the maps as 6 Ononis, which 
has long been known to consist of four component stars. Prof. Struve, of 
Dorpat, detected a fifth, and a sixth has recently been added to this remark- 
able set. Here we have an example of six suns, probably, in physical union, 
and revolving about their common center of gravity. Near these six stars, 
and between the short point of light and the long projecting branch, there 
appears to be an absolute vacuity, intensely black. Whether this be an 
effect of contrast with the brilliancy of the nebula, or occasioned by some 
peculiar constitution of this region, it is impossible to determine. In exhibit- 
ing this object to persons who had never seen any thing of the kind, I have 
frequently heard them remark, that a part of the nebula was hid by a black 
cloud. 

Sir W. Herschel being unable to resolve this nebula, with his most power- 
ful telescopes, placed it among those which he regarded as probably composed 
of the nebulous fluid, or chaotic matter. The subsequent investigations of 
Sir John Herschel confirmed the views of his father, and it has only been on 
the application of the six feet reflector of Lord Rosse, that the true character 
of this object has been ascertained. The space penetrating power of the 
monster telescope has carried the observer near enough to discern the in- 
dividual stars of which it is composed. Its resolution has also been accom- 
plished by the magnificent Refractor of the Cambridge (U. S.) Observatory. 

The distance and magnitude of this object, as thus determined, absolutely 
overwhelm the mind. In case light be not absorbed in its journey through 
the celestial spaces, the fight of the nebula in Orion cannot reach the eye in 
less than sixty thousand years, with a velocity of twelve millions of miles in 
every minute of time ! and yet this object may be seen from this stupendous 
distance even by the naked eye ! What then must be its dimensions 1 
Here indeed, we behold a universe of itself too vast for the imagination to 
grasp, and yet so remote as to appear a faint spot upon the sky. 



332 DESCRIPTION OF THE TELESCOPIC VIEWS. 

The resolution of this nebula has been the signal for the renunciation 
of Herschel's nebular theory, by some of its former supporters, with what 
reason I know not. Herschel only gained the first idea of his great theory, 
after resolving nearly all the previously known nebula, and now it is to be 
surrendered because a solitary one has been unexpectedly resolved into stars. 
The theory can hardly yield on such easy terms. 



PLATE VIII. 

Nebula in the Shield of Sobieski. R. A. 18 h. 11m. Decl. S. 16° 16'. 
This is an irresolvable nebula, figured by Sir John Herschel, during his 
residence at the Cape of Good Hope. Its favorable position, as seen in 
southern latitudes, enabled Herschel to trace the outline of the nebula much 
farther than any preceding observer had done. The singular figure of this 
object, seems to suggest some power of attraction operating on the particles 
of matter, or the stars of which it is composed. In one place we see a bright 
condensed mass of light, nearly round, while it is encircled by a perfectly 
dark vacuity, on the outside of which nebulous light is again seen. The 
smaller curve, at the opposite extremity, was discovered by Herschel while 
at the Cape, and has not been seen at any northern observatory, so far as I 
know. The stars scattered through this nebula are not, probably, connected 
with it, but accidental in their position. It is impossible to assert, with cer- 
tainty, the absolute nebulosity of any object. It may be that higher powers 
will resolve even this one into stars, but thus far there has been no evidence 
gained of its resolvable character. 



PLATJE IX. 

Nebulous Stars, and Stars connected with Nebulae. 
Staiis are sometimes found in the heavens surrounded by a hazy light of 
great extent, in the center of which the star is placed. It was an object of 



DESCRIPTION OF THE TELESCOPIC VIEWS. 333 

this kind, which first suggested to Sir W. Herschel his great theory of the 
formation of suns out of a nebulous fluid. He thought it impossible to 
account for the central location of stars, surrounded by nebulous matter, in 
any way except by supposing this to be a sort of atmosphere attracted to, 
and sustained in its spherical form, by the power of the central body. I have 
examined specimens of these objects, and always with increasing wonder. 
Their magnitude must be enormous, as the stars are certainly not nearer 
than other stars, and yet the circular halo around them is of a diameter 
easily measured, and proves them to have a circumference, perhaps, greater 
than that of the entire orbit of Neptune. 

Specimens are found, in which there is but a mere condensation of fight 
in the center ; others in which this central light is brighter, and so up to a 
perfect star, with the surrounding haze. 

In some instances the star is found with a stream of fight issuing from it, 
resembling the tail of a comet. These are, certainly, objects of very difficult 
explanation, in case we abandon the idea of nebulous matter. 



PLATE X. 

The Great Southern Cluster. 47 Toncani of Bode's Catalogue. 

This remarkable object was resolved by Sir John Herschel, while in the 
south. Its position renders it invisible in the northern latitudes. There 
seems to be a curious change in the law of condensation, presenting three 
successive stages, Herschel regards it as a globular cluster of vast extent. 
There is said to be a marked difference in the color of the central portions 
and the exterior stars. The interior is of a rose color, while the exterior is a 
pure white. The stars of the southern heavens are said to present a greater 
variety of vivid colors than those of the north. Yet in the north there are 
some beautiful specimens of double stars, in which vivid colors are beautifully 
contrasted. Orange and blue are of frequent occurrence ; red and green are 
sometimes found. In the double star Antares, the principal component is 
orange, while the small companion is decidedly blue. 

The condition of planets revolving around a sun whose light is orange 



334 DESCRIPTION OF THE TELESCOPIC VIEWS. 

or red, associated with another sun, whose light is blue or green, may be 
more easily conceived than described. The exquisite mingling of hues, pro- 
duced by this double illumination, must exceed any thing within the limits 
of the changes of light due to our own planet. 



PLATE XI. 

HerscheVs Section of the Milky Way. 

This figure represents the form of the figure, cut from the Milky Way by 
a plane passing through the sun, and perpendicular to the two streams, in 
which this stratum of stars is divided. The branch extending from the 
bright spot in the center to a, is the section of the upper stream, while that 
extending to e is cut from the lower stream. The bright points representing 
stars, it is manifest, that on the hypothesis of equal distribution, the greatest 
number of stars ever counted in the field of view of the same telescope, 
would be when directed along the line to e. 

The bright central spot represents the sun's position in the stratum, 
and its circumference limits the range of penetration of the naked eye ; so 
that all the stars exterior to this small, bright spot, are only to be seen by the 
aid of the telescope ; and yet the eye, according to Struve, reaches stars so 
remote that their light would stream on for one hundred and thirty-seven 
years, if they were now struck from the heavens ! What an idea does this 
figure present of the vastness of our " island universe ! " 



PLATE XII. 



Hie Ring Nebula, in the Constellation Lyra. A. K. 18h. 47m. Dec. 
32° 50'. 

The remarkable size and form of this remote object, have combined to 
render it one of the most curious and interesting in the heavens. It is beau- 
tifully shown by the Refractor of the Cincinnati Observatory, and appears as 



H 



DESCRIPTION OF THE TELESCOPIC VIEWS. 335 

a ring of misty light hung in the heavens, with a diameter as large as that 
of the moon, when seen with the naked eye. In instruments of inferior 
power, the interior of this ring appears quite dark ; but I have always seen 
this space filled with more or less light, according to the purity of the atmo- 
sphere at the time of examination. 

It is supposed to be a vast congeries of stars, united into one grand system. 
This object is so remote, as to be utterly invisible to the naked eye, and its 
light cannot reach us in less than twenty or thirty thousand years ! 

It has shown symptoms (as Herschel remarks) of resolvability ; but has 
not been fully resolved. There is one other ring nebula known in the 
northern heavens, and, I believe, but one. Herschel has found several in 
the south. 



PLATE XIII. 
Great Southern Nebula, No. 30 Doradus. A. R. 5h. 40m. Dec. 69° 11'. 
Hehschel describes this as one of the most singular and extraordinary 
objects in the heavens. " It derives no small addition to its intrinsic interest 
from its situation, wliich is among the thickest of the nebula? and clustering 
groups of the greater Nebecula, of whose total area it occupies about one 
five hundredth part. It contains a large number of stars probably not con- 
nected with the nebula.'" 



PLATE XIV. 
A large Elliptical Nebula in the Constellation Andromeda. 



PLATE XV. 



A large Nebula in Sagittarius ; figured by Sir John Herschel. A. R. 
17h. 53m. Dec. S. 24° 21'. 

I have frequently examined this beautiful object. It exceeds in magni- 
tude all the nebulae visible in our latitude, except that in Orion. It is fol- 
lowed by a brilliant, coarse cluster of stars. 



336 DESCRIPTION OF THE TELESCOPIC VIEWS. 



PLATE XVI. 

Lord Rosse's Whirlpool or Spiral Nebula. A. R. 13h. 23m. Dec]. 
48° 02'. 

This is certainly one of the most wonderful objects in the heavens. I 
have frequently examined it with the Cincinnati Refractor. The principal 
outlines are well shown, but the filling up is only accomplished by the 
monster refractor of the Irish nobleman. The two great central clusters are 
seen with my large instrument, and were originally drawn by Herschel as 
distinct objects. The curious spiral form is exhibited with great beauty, and 
seems to indicate the action of some powerful and controlling law, in this 
remote body or cluster of universes ; for such indeed it seems to be. 



PLATE XVII. 



The Dumb-hell Nebula, as figured by LnrdBosse. A . R. 1 9h. 52m. Dec. 
22° 17'. 

This object was discovered by Messier as early as 1764. It occupies one 

of the richest portions of the heavens, and is surrounded by thousands of 

■ 
stars. In ordinary telescopes it may be seen in the shape of a double-headed 

shot, or dumb-bell; hence its name. With more power its outlines are 
changed, until, with Lord Rosse's great telescope, it is seen under the figure 
shown in the plate. I have seen the object very nearly under the form in 
the drawing, but cannot say that I have ever fairly resolved it into stars. 
The Cambridge refractor, in the hands of Mr. Bond, is said to have accom- 
plished its resolution. I see many stars on the nebula, but presume them 
to be accidental, or located between the observer and the nebula. 



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